The ability to consume the power of magic items and convert that energy into special powers is the domain of those known as eaters of the arcane. Eaters of the arcane are a rare breed and few of them survive once they descend down the path of magic dependence.
While not evil, eaters of the arcane are most definitely not good. These spellcasters, surviving off of power drained from magic items, are substance abusers of the worst possible kind. Few eaters of the arcane manage to shake their addiction and those who do carry the scars of their former addiction for life.