Well, Wisdom doesn't seem to have much practical use. I suppose a maximum of 12d6 for Fireball on someone with 14 WIS is nice, but by 12th level, I'll have a spells with much higher level caps anyways. It makes it especially ironic that Clerics/Druids would now have virtually no use for Wisdom; their cap increases are generally quite meager, and most spells with multiple targets will either affect the whole group or are area effects.

Charisma can be bypassed my using no-save spells, if desired. I find it ironic that Summoners (who regularly interact with summoned creatures) will be the ones most likely to dump Charisma. Clerics/Druids once again won't care when simply buffing - take a look at the Archivist for a current example. Also, the idea of "unwise but highly sociable wizards" feels completely off to me.

Intelligence is now something everybody wants, meaning that most spellcasters become INT/WIS or INT/CHA. Druids are now simply INT-SAD rather than WIS-SAD, changing little. Wizards and Sorcerers (and Bards) are very sameish, having the same stats and spellcasting capabilities.

While I don't think it's a bad idea, I do think that this is not the method you want to persue. It would make more sense to tie the spellcasting method to another relevant stat (DEX for arcane casters for finger manipulation, CON for divine for channeling energies?) that attempting to split all spellcasting between the three types of mental stats. Also, as someone said earlier, the "Wizards rule Fighters drool" is primarily under optimal conditions - mid level, 4 encounters a day, full knowledge of upcoming events. The more you deviate from that, the more important the non-SAD stats become.