Ebon eye doesn't appear to directly affect casting, just the ability to see clearly in certain conditions...why couldn't you put this on, say, a Gunslinger or Ranger to limit their ranged attacks in bright conditions?
Most spellblights specifically affect spellcasting in some way, but Ebon Eye seems like a generic kind of curse that could hamper anyone, not just casters...if you were putting it on someone with Bestow Curse or Major Curse, I would think that, since it is the right power to be such a curse, you could put it on anyone (Most spellblights, you wouldn't bother putting them on someone like a barbarian, since they specifically mess up casting.)
I guess Spellblights make pretty good ideas for the curse spells. I would probably be cool with that.