For instance: Using Cure II as a Gladiator would cost them 80MP, but for a Conjurer, it would cost about 40MP. Then...maybe while you're a Paladin, it would cost less since that job will have a stronger focus on white magic than a Gladiator would.

And maybe the higher your Conjurer rank, the less MP it would take while you're in a different class. They could possibly introduce a skill mastery system. The higher level your skill is, the more useful it is while you're in a different class. Ah, idk, these are just some ideas.

P.S: they should totally give us the traditional names for spells (cure ii = cura, cure iii = curaga, curaga = curaja?)