spells: higher lvl = more sp used

[Logwad]

I've noticed that as you gains lvls in the various spell skills that spells cost more to cast.

Whats exaclty the dealy-o with this? some questions I have are:
1. do all spells do this?
2. are the spells more powerful because they use more sp?
3. whats the real advantage of using more sp if the are more powerful. isn't that just like being able to cast 2 really powerful spells rather than be able to cast 3 spells which end up doing the same damage? I'd rather cast the 3 spells, so I can control how much sp I use.

[Ryo]

Damage/range/raw power increase with level, so it's just right sp cost too should go up.

Also, since leveling up gives you more max sp, it's nice to balance the number of spells you can cast.