The crystal level limits are simply a bad solution.

The real problem with game imbalance is that its really easy to have 1 high level guy buff your abilities to be godlike at your current level.

How do you fix that?

The simple answer is to follow the rules put down by the who can attack who code in the 25% zones. If you can't attack a player (as if they were in a 25% zone) then you can't cast on them either.

Could big buffing still occur? You bet! But If you limit the duration of buffs to 5 minutes then its not likely to occur very often. If it does then they have earned it. For example:

Player1 Level 15
Player2 Level 20
Player3 Level 30

Player 3 could buff player 2 who could buff player 1 and give them a bigger buff than normally possible. BUT this requires some coordination of three players. If people want to do it they can, and should be rewarded for the extra effort.

The other thing this helps to fix is those damn RED healers who keep the guy who's green to you alive. It works both ways...I took on 5 clanners in their arena and killed 2 of them because of a deeply red healer was healing me. They never came close to killing me!