dtgreene: Actually, the effect I am talking about, I'm pretty sure, raises *all* stats to 25 to the *entire* party.
In particular, I am talking about "spwish08" (assuming the IESDP list is accurate), not "spwish29".
Hickory: You're right, that spell does exist -- I'd never come across it. But it's so insanely overpowered that the percentage chance of getting it at all must be infinitesimal. There's only 2 possible Wish scrolls in BG2 (Watcher's Keep), so even Simulacrum and Project Image are not going to help, and who wastes a level 9 slot with Wish?
According to a .2da file included with GemRB, this effect requires 15 Wisdom to get, but otherwise it doesn't seem particularly more rare than any of the other good effects.
If you are using it for spell learning, these issues are not a problem; if you fail to get this effect before running out of spells, you can just rest and get your spells back (including any Project Image/Simulacrum effects). Don't forget that you can occasionally get free potions or wands this way (in Icewind Dale: Enhanced Edition, I was able to get a Potion of Superior Healing, which doesn't exist in the original IWD).
If you are using a Sorcerer, you can spend a 9th level spell pick on Wish, and then have that spell available if you need it without compromising your ability to cast other 9th level spells (at least until you run out). This can be very helpful, as Wish is the sort of spell that can save you in an emergency (for example, by reviving your entire party), but isn't needed in non-emergency situations (though it can be fun, especially if you have 18+ Wisdom to increase the chance of good effects).
Also, this effect doesn't seem too overpowered to me; Strength and Dexterity can be raised to high values in other ways that last longer (don't forget potions!), Constitution above 16 doesn't help non-fighter-types (and the regen effect isn't as good as the Restoration/Resurrection effects, plus that only matters if you happen to rest while it's in effect), and the Wisdom effect doesn't last long enough for you to actually memorize extra spells. More powerful effects include the one that restores your spells (which can give you more wishes), and the so-called Time Stop + Improved Alacrity effect (if you are not playing the EE, set auto-pause to "spell cast", cast Improved Alacrity, and now you get both 0 cast time and the removal of the 1 spell per round limitation, so you can now cast all your spells in 0 time).
(Side note: Did you know that the genies summoned by Limited Wish and Wish count against your summoning limit?)