I know this might garner me some hate but after all this is a cRPG - we need to use the fact that this is different from a pen and paper game and use what is available to us.
On the subject of buffs, I think that Guild Wars had a pretty neat system when it came to them. Assuming that we are using mana pools, then each buff could slowly deplete the mana pool over the period of time that a buff is sustained. More buffs means that the mana pool depletes that much faster.
Since that was an example of a magic mechanic that didn't annoy me, I guess I should post something more on-topic. I didn't see the point of using the Vancian system if it was an easy matter of resting 8 hours right after the fight. Don't get me wrong, I like the Vancian system, but if it is implemented, it shouldn't be trivialized by another mechanic.