I've rarely found skillups to be rough on most casting classes. Healing skillups? Fight some undead. Gusgen mines has L86-89 skeletons that are perfect for this kinda thing at the top, but there's plenty to be had on the way up. Enfeebles? Worms. I can walk into Dangruf Wadi, Silence a Witchetty Grub and just cycle debuffs on it while it sits there, harmless.

A system that rewards slapping EP's around from 15th or so to 99 is always going to have skillup issues. The solution for mages is easier than it looks, though.