The one thing I don't like about the various blasting 'At Will' powers is that because they are so easy, and unconsequential to the caster, that a fair amount of the mystery is lost from the game. I want the casting of magic to be taxing in some way, or at least be an issue of resource management (as it was).
I'd like spells to be quite hard to find, and written in dusty old tombs - awaiting an adventurous Mage to discover in some old ruins somewhere. I'd like it if a character's spell list was built up slowly over time, and that spells were given interesting, colourfully descriptive names.
I'd also like to move away from simply describing effects, and actually put in a bit of paradigm around the way magic works. It doesn't have to be complex, I mean the notion of Vancian magic (complex formulas stored in mind), is actually a paradigm as such, as is a Cleric calling upon a god. But if we are to have different magic classes, and systems, have them being described in ways that are less gamist and power-application driven. Encourage a teeny bit of philosophy to come into the game.
I'd also like some more creative rules for designing magical items and new spells - although this could be held back for later books outside of core.