One idea I did consider, which I ended up not using because I didn't have time to playtest it, was the idea of removing the elements altogether, and just having the spell lists. To balance this out, though, spellcasters would have a certain number of skill points which they'd use to become increasingly good at different spell types. They'd have to make casting skill checks whenever they cast a spell, and we'd do away with MP altogether. So you'd be able to cast a few weak and simple spells at low level with a good chance of success, and at higher levels you'd be able to cast tons of spells each day, but none stronger than maybe 5th level.
As I said, we don't have time to playtest it, but I think about it occasionally and wonder how it might have worked.