Actually, bards don't get psionic spells either; they only get mage spells, so changing into a bard won't let you continue learning psionic spells. Maybe you meant monk?

Also, it's worth noting that leveling up from level 1 to 10 takes fewer experience than gaining one level after reaching level 11, so a level 10 class change would only cost you just under 1 level in the long run.

Alchemists and Valkyries need the same XP to level up, so an Alchemist who never changes class will always be ahead of a character who changes into Valkyrie, assuming the Valkyrie earned at least one XP before changing into one and the Alchemist didn't end a battle dead.

Oh, yes, I meant monk, not bard! I don't know how I made such an egregious error! Must be the dungeon air.... :-)

Considering how fast he will be able to level up, even doing very little, and the SP I can get from it, I guess I may just take the plunge to lord for him and see how things go from there.

I'm still not sure now what I'll be doing with my other characters, but I have at least a little time to think about it while they're wandering the mines gaining EXP.

Hybrids are better than casters at the same level, a ranger will do about 4 times as much damage with physical attacks than an alchemist. And class changing will yield more spell picks and mana.
But you don't need the perfect powergaming party, alchemists level faster than rangers so monsters will have an harder time to resist those spells.
For perfectionism you could switch to ranger and then finally to ninja for AC and kirijutsu and AC but 3 ninjas and a monk might feel boring.

If you keep your alchemist pure she'll level the fastest. But most other classes level slower.
Valkyrie/alchemist need 563,200 XP to reach level 11 + 312,000 XP for each level afterwards.
Ninjas need 768,000 XP for level 11 + 475,000 XP for each level afterwards so the valkyrie 8>ninja 8>valkyrie would overtake in spite of the extra XP spent.

Bards get up to 3 attacks per round at high levels, that's 2 main hand attacks per round you can use with a polearm like quarterstaff.
Any class can attack from the back with a quarterstaff or even better polearms. One-handed polearms even allow combining with throwing weapons.
For no class it's worth putting skill points into weapon skills (including fists), they can be maxed simply by using them, the lower they are the faster they will rise.

But in Wiz 7 you were (to my annoyance) forced to spend some of the skill points on "useless" weapon skills, which encourages class changing to get those precious magic skills, especially if you start with imported prestige classes.
But if you change to basic classed at the start of Wiz 7 you can no longer use some of the best weapons...choices&consequences, I guess.

Yes, but you can then change back after gaining some levels, at which point your spellbook skill should be high enough to learn higher level spells. Also, keep in mind that you don't have to (and probably shouldn't, actually) change everyone at once.

Also, there is no such thing as a "prestige class" in the Wizardry series. In fact, Wizardry 6-8 allow you to start characters as any of the 14-15 classes in the game.

There are a few other differences in Wizardry 7 as well. For instance, at high levels everyone needs the same amount of XP to level up, so Valkyries no longer significantly outlevel Ninjas. Also, Valkyries level a bit more slowly, Priests a bit faster (faster than Valkyries now), and Alchemists slower.

Of note, Bishops aren't that good in Wizardry 6/7, but if you are planning on importing your party to Wizardry 8, it is a good idea to have a Bishop at that point; Bishops are the best class in Wizardry 8.

Yes, that would most definitely be boring. If you grind enough, I suppose you could eventually create a party in which everyone is a ninja with every spell available; but in addition to being terribly boring, it would also take all of the fun and challenge out of the game. And if you're not having fun playing, then there's really no point.

I wasn't terribly impressed with the ranger I had in my party before she changed to a bard, so I'm not particularly attached to the idea of changing my alchemist into one. I was only planning it because I was led to believe that you need all hybrids by the end of the game, and that no character should still be a pure spellcaster after Lv.10 (and ranger would keep her in the alchemy school while also granting ninjutsu). But based on what you guys have written, I'm not sure I believe that anymore. I do think the game would make more sense if mana regeneration was tied to current character class rather than starting class, and maybe spell power too, because it feels like there should really be some incentive to remain a pure spellcaster.

I'll have to get a polearm for my bard. I've discovered that every type of bow I've found so far is absolute crap. Even slings with razor stones do better damage! Interesting, I did discover that the queen's bullwhip can also be used from the back row. Although not a very powerful weapon, it does generate some interesting images in your mind, particularly if the character wielding it also has the stud-cuir bra+2 equipped!

It's a good thing you don't anymore. Each of the 3 party suggestions in the official cluebook includes 2-3 non-hybrids.
I've even seen a printed walkthrough in a magazine where the writer had played through the game without any hybrid classes at all.
Class switching wasn't considered either, its official purpose was being able to reach classes you don't have the time to roll for, the developers didn't think about the exploiting potential, the game difficulty was balanced for doing without.

I never really thought about it that way. It's true that with all of the information about the game calculations and everything out in the open these days, most of the online recommendations of how to build and develop a party are all about exploiting the mechanics, which is really not playing the game as it was intended. Still, being able to understand how the game processes and calculations work is a good thing, and I also think being able to edit things with the Cosmic Forge utility is good, as long as one doesn't go overboard making things too easy, which I feel would ruin the game -- because then where's the sense of achievement, or excitement about special discoveries or bonuses? I feel that maps and walkthroughs are best used only to check and make sure you didn't make a mistake (like if I screwed up a block on a map, which starts driving me crazy, I'll reconcile it with an "official" version to fix it rather than retracing my steps 100 times). In the end, the game is really all about having fun, so I strongly feel you should play however is the most fun for you (provided it is possible to do so and still finish the game). This may be different in multiplayer/online games in which you're playing with/against others, as the way you play will affect others' enjoyment as well as your own. In that respect, I am very happy with all of the choices I've made so far because I did them for the purpose of enjoying the game more (and have succeeded in such!). And of course I do also want to develop characters I can feel proud of, and use successfully in the subsequent Wizardry games.
In addition to reaching classes you couldn't roll initially, another purpose of class changing indicated in the manual was simply to try something new if you weren't happy with how your character was moving along in his/her current career, and needed a change of pace. When a character starts to feel like he or she is stagnating, a class change is a very refreshing thing indeed! (I've felt that way after every class change I've made so far.) And then any player who tried out a class change would immediately see the benefits of it, so even back when the game was initially being played years ago, people must have come to realize that this could be a good way to build a strong party.
As an aside, I took your recommendation and changed my dwarf to a lord a couple nights ago, and it has been a great change! I had obtained one of my most desired psionic spells just before the class change (Psionic Blast), and even as a lord he's been very successful with it, driving enemies insane, quite literally -- with miner dwarfs dancing uncontrollably, monstrous bats babbling incoherently or turning on each other, and such. :-) I've been putting all of his SP into theosophy - which is up to 82 already - and he gets two swings from the back row with a special lord/valkyrie only weapon that I picked up from Smitty. I do feel a little bad/guilty when the time comes to pick a new spell, and the choices are so puny because I didn't put any SP into theology. This has started to make me wonder -- do you think without ever class-changing my valkyrie, and with no other characters learning theology, I'll have enough access to priest spells for later in the game?
Now I'm leaning towards not class changing any of my ninja, valkyrie, or alchemist (with the caveat mentioned above regarding priest spells). I'll most likely be changing my faerie samurai to a faerie ninja at her next level up. And what's cool is she can probably keep using the katana and wakazashi she's using now! She could be the ninja who uses special weapons, while the other one only uses hands & feet. The biggest hit for her will be the loss of her current 16 STR; I may need to use strategic level-ups/reloads to make sure she gets it back again.
I'm still not sure whether or not to class change the bard to a samurai, or stay as a bard. Instruments are fun, and don't require MP, but then I imagine they will start taking up a lot of inventory space too, and maybe even get heavy. Plus I will be without a samurai after Melody class changes (though either way the bard/samurai will be the de facto party mage). I guess I could just play as a bard a while longer and see how things go. She should be eligible for the change at next level up (only 1 stat. point away), but that doesn't mean I have to make the decision right away.

One other nice use of class change:

Without class change, it might be hard to see all the spells the game has to offer. By class changing, you can more easily fit all the spells into one party.

Of course, it would help if the Alchemist and Psionic spellbooks were more useful, but at least that was addressed in Wizardry 7 (we now have spells like Death Cloud) and 8 (Toxic Cloud, Hypnotic Lure, and a uniquely useful Psionic Blast). (Of course, in 8, class changing is a much worse strategy than before; if you want to see most of the spells the game has to offer, you want a Bishop, which has been drastically improved from being one of the worst classes to being perhaps the best.)

One other good use of class change; apparently, in 6 or 7 (don't remember which), fighters take double damage from enemy physical attacks; if you run into this bug, you can class change the character into a class that doesn't take double damage.

Since no one ever seems to have experienced this while playing I suspect it's just a myth introduced by the cosmic forge editor.

More than enough. With 7.5 skill points average per level up, a fast levelling class like Valkyrie should still get about 40-50 skill points to waste after maxing theology. The low level spells armorplate and enchanted blade are the only important ones you need priest spell casting for.

I'm still considering possibly temporarily class-changing her to ninja, and then back to Valkyrie because I realized I could change back after gaining three levels or so; and since Valkyries level up so fast, she'd probably catch up to the others in no time. Early in the game, I didn't realize that skill points would be auto-allocated to class "preferred" skills, so I did lost a lot of SP then since I think my Valkyrie fought with everything but a pole or staff. If I do this, then the alchemist will be the highest level character, and nobody will be able to catch up to her.