I'd like to touch upon a very nice idea I saw in Novus RPG (hoping that mentioning a game written by Tim Dugger will not start hard feelings) : spells are arranged in Spheres as in HARP (except it's another word, but the notion remains the same), but they also have a keyword that describes the general type of spell: sample keywords are "Ward" for defensive spells, "Divination" for information-gathering spells, "Heal" for healing spells and so on.
I seem to remember someone complained that a mage could throw a fireball but not heat up a nice cup of tea. (And someone else replied that spells are fixed techniques that allow for one specific effect, not an array thereof. Which I disagree with, as most spells can be scaled up in various ways, not counting the various ways in which talents alter spell effects.
So I'd like to propose that every spell gets associated with a Domain: Arcane Bolt with "Attack", Divine Hammer with "Boost", Long Door with "Movement" and so on. And for every level you learn in a spell, you get a cumulative +1 bonus for casting freestyle spells in its Domain.
Another possibility would be to list more than one Domain with some spells (Elemental Bolt (Fire) getting "Fire" and "Attack"), and the player chooses which Domain gets the aforementioned bonus.
Oh and by the way, could it be possible to scale down some spells? The most obvious option would be to have spells with a Touch range cost 1 PP less when cast with a Self range.
Note that scaling down might also cost more PPs: say you want to cast an Elemental Ball on three enemies who threaten a friend of yours, but there is no geometric way that you can fit the three hostiles in a 10' radius ball without one of your friends being caught in it too. (And they are really threatening, so you can't take the time to Elemental Bolt them in the face. Actually, say you don't even know Elemental Bolt. Only Elemental Ball and other, non-aggressive spells.) You might want to throw them a 5' radius Elemental Ball, which could scale up the spell because it's actually more difficult to release the elemental energy on a smaller area.