wow this thread got big when I wasn't looking. Meant to read it all before posting, but it's a lot of stuff to read. As I skim, I see a lot of folks have my same opinion.
Being an old-schooler, I've always liked the "Vancian" system. It might just be that I was raised on it, or might be because it offers a certain "feel" that other games don't possess. Call it one of my "sacred cows" if you must, but if it's not Vancian then it doesn't feel like D&D to me. This is one of my biggest issues with 4e. But wait...
One thing I always hated was having to waste spell slots on stupid things like detect magic, read magic, write magic, scribe, etc. Some things are just things a learned magic-user should be able to "do," no matter what. And as a magic-user gains in ability/level, the amount and type of things he should be able to just "do" should increase. So I offer a compromise.
I think DnDNext can benefit greatly from both systems. A combination of the two, really. Allow a small series of at-will, hourly (I wouldn't call them "encounter" powers... that seems an artificial measurement of time that lends itself to a board-game feel rather than an immersive roleplaying experience), or daily "powers" that a magic-user has access to. Allow the player to choose these powers at start. Otherwise, spells are memorized/prepared and studied for and are Vancian in nature. As a magic-user gains access to a new Vancian-type spell level, allow another "power" selection. This way, you have a character able to do the small stuff basically whenever he wishes ("powers") and able to cast the potent magical spells with study/preparation/dedication ("spells").
This could also be one major distinction between divine magic (which would be mostly granted "powers" and fewer Vancian "spells") and arcane magic (which is fewer granted "powers" and mostly "spells"). Of course, the two would have to have completely separate power and spell lists, as is always the case.
I, an admitted old-schooler, would not only accept but fully embrace this compromise of concepts.