Seeing as the magic system seems to be discussed a lot, I wanted to add another suggestion:
How about keeping the Vancian system (possibly adapting it a little bit), but also developing one or two alternative magic systems so that each group can choose from two or three magic system whichever one it prefers?
Just an idea.
I think Pathfinder or 3.75 rules could be more usefull if they suggest such kind of rules. Paizo already done the same think with the xp rules.
They could develop 3 base system : Vance's, Point's system (like Psion or channeler at Midnight) and Skill system.
More than a new game, more than a rules-suggested-book (like Unaerthed Arcana ), Pathfinder could propose few rules to modify and improve 3.5
Unearthed Arcana had options for different options for spellcasting. Maybe different classes can have different rules for spellcasting, showing a game mechanic behind sorcerers(skill based) casting spells through ability and wizards casting through study(vancian system). This way those who like the vancian system can play wizards and those who like the new system can play a different class and they both sit at the same table but play at different rules.
The problem with these suggestions are there's a book called Spell Compendium.. and there's another book called Relics and Rituals.. and a Relics and Rituals 2.. and dozens of other 3/3.5 spell books that I want to be able to use and if Paizo goes mucking around with Wizard and Sorcerer those of us that bought them won't be able to use them.
Pathfinder RPG is supposed to be as backwards compatible as possible. If you want to use an alternative system published in another book, keep doing so.