Although it has already been said, a good way to get spell-casting warrior's magic kick started is to put points into realm skills. I'd say raise important realms to at least five, if not level ten, before letting them develop through use. It has worked wonders for my rawulf ranger in my current party.

On that note, piety is very nice for hybrids. Anyone who has played a lot with these classes should have noticed it with the magical development of the soul shield casters. In that vein, humans are typically the best choice for spell-casting warriors, easily. Nevertheless, there are other useful race choices. Depends on what one is intending on doing and character feel, of course.

This might help with an all hybrids party. But it does mean letting martial prowess stagnate a bit during Arnika road, I doubt that's too much of an issue, honestly, but I'd have to give it a try. But I'm busy with my current magic heavy party, and I feel like challenge parties aren't for me. I do like testing the waters, and it's a great way to learn mechanics, but actually going the full mile is often boring, for me. I'd still recommend challenge parties, and my current party is rather gimmicky.

Not that anyone cares, but my current party is a rawulf bishop, dracon alchemist, dracon priest, dracon gadgeteer, rawulf ranger, and felpurr fighter. Not the strongest party, but once it gets going, it is rather strong. Plus, the bishop and ranger help make further character building entertaining.

Assuming Wizardry 6 or 7 (because you didn't specify):
* Starting as a full caster can be beneficial, as that way you get a head start on the magic skill, which is what you really want to raise (particularly since it *doesn't* increase through use).
* In fact, doing so may help the character's fighting. If you start as a Priest, reach level 2, and then change to Valkyrie, you will get some accuracy for reaching level 2, have more as a level 1 Valkyrie than you would otherwise, and because your highest level is 2, get more accuracy *again* when you get back to level 2.
* In general, class changing is the key to qualifying for higher level spells, but you do eventually need to stay in a class and reach higher levels to handle harder battles and use the spells at higher power levels.
* Also, in Wizardry 6 at least it's easier to boost your magic skill if you get any skills that your class automatically increases to 51, so that you can instead allocate those points to the magic skill.

Note that Wizardry 8 is completely different here.

Oh hey, my ranger hit alchemy 30 before level 9. This is the way. Well, let's wait till we get to the swamp before celebrating, yes?

Oh, that's another thing about magical development. If one doesn't want to spend the time power leveling—just constant use—geting magic schools to twenty-four is often good enough for specialists. For warriors and bishops, however, leveling schools to forty-five, with points, might be worth it. It certainly makes it easier for bishops to get level four spells by level nine. For the thieves, it's not neccesarry to pump up the skills. But, putting five points into music isn't a bad idea, since it makes it that much easier to get the skill required for the piercing pipes. Likewise, a gadgeteer that is rushing towards the swamp might want to invest some points in, but I'm not sure how many. My current gadgeteer has over thirty engeneering, enough for the lava lamp once we reach Trynton.

For Wizardry 8 (which you should have mentioned, since the board is for more than one game), there seems to be certain key points where it becomes easier to level the skill further on its own.

* Wizardry: 15 for the non-combat spells. You'll want to eventually raise it to 45 for X-Ray. (A Bishop typically needs a bit less due to Mental Magic skill growth from identifying items.)
* Divinity: 30 for the non-combat spells, 60 (usually a bit less) for Heal All. Heal All, at the auto-recast power level, will repeatedly cast at PL 1, leading to fast skill increases.
* Alchemy: 40 to start mixing Cure Disease potions, which give fast skill increases. At 50, Renewal potions also give fast skill increases, and can use those Cure Disease potions you've already made and not had an opportunity to use. 30 gives you Chameleon.
* Psionics: I'd say 30 for Chameleon and Hypnotic Lure, both of which can be used outside of combat.

30 is plenty for a Gadgeteer to start being useful with gadgets. Even 15 is enough to start using Guardian Angel.