Yeah, but it's annoying if you are just waiting for an SP recharge and you get all your spells removed 'cause you aren't using them.

NOTE: because of the posts on this thread I have come up with 4 new spells which are coded and 3-4 more that need to be coded still:

Chain Lightning: Jumps from target to target doing damage.*

Lure: (Extra cost of 1 apple) Attracts mobs to it as it moves. It then stops for a while, then dissapears.

Medusa Gaze: Turns a target mob into a rock for an amount of time based on the caster's level. Rocks can't be attacked or move.

Lightflame: Bolt spell. Damage is added to your health as it is subtracted from your opponent's.

Nova: Damages every enemy around the caster.

Inferno: (extra cost: drake or dragon blood) Damages every mob inj a range of 6 squares, including the caster.*

Poison strike: (extra cost: Vial of Venom) Every enemy that you do damage to while the spell is active suffers from poison (damage every few seconds).

--Vito

Well, if you were to make a summoning idea, I think you should only allow the summon to exist while the player has MP :D.
And, for example, larger summons could require more MP at a time to keep them alive. I think that is a good idea.

It could also work for spells like Fire. You could select a power level of it, and the higher the level, the more damage, but at the cost of more MP to keep the fire going farther.