There has been a fair amount of talk about different methods of magic in fantasy games. Vancian magic (fire and forget) is really treating spells like artillery shells- only a limited number of them, and when they run out the fearsome magic user is suddenly just a weenie in a bathrobe. So being a magic user becomes a minigame in resource management... how to use your limited arsenal most effectively.

Spell points aren't much different, except that they are more flexible. Now the spells are like guns, and the magic user has to decide which gun to fire his limited supply of bullets through. More flexible and easier to grasp, (especially if you have played a fantasy video game or MMORPG) but also kind of generic.

Magic is in essence a mage hacking reality (According to White Wolf anyway) so each spell should be a fundimentally different tacktic. But why should the mage not be able to repeat that trick again. But if a magic user is able to bend reality to his will anytime he wants, then why wouldn't he?

Call of Cthulhu (which used the spell point system) had the additional counter balance of sanity loss when fiddling around with magic. And there have been systems that have significant risks from spells backfiring, although I am not thinking of any titles off hand.

One option would be a modified Vancian system where a mage has to roll a saving throw after every time they cast a spell a day. They throw a d6 for how many times they have cast it that day, (including the current casting) and then if they get a total of 6 or more then they 'hit the wall' and cant' cast it again till they rest. Either mental exhaustion, or some sort of abstract power is used up... or maybe the tiny demons on the other side have noticed this activity and are tearing at the mage's soul.

Example: the first time a mage casts fireball, they roll 1d6, and will succeed on a 5 or less. The next time they cast it the same day, they roll 2d6, which will statistically fail (7 being the mean). The third time, they roll 3D6, etc...

One option might be to allow the mage to add the difference between their level and the spell's level to limit. (so a 5th level mage casting a 1st level spell for the 3rd time would roll 3d6 and try to get a 9 (5+4) or less.