Given that it now would take up inventory space, this would leave it a very niche item. Basically for Goo Blobs and equivalent bosses only, which most of the time would be a shop-waster. That's why I think it should offer magic damage above your regular attack is the right way to go. This makes it a useful item even if you aren't facing enemies with resists. Also, this would make it the only damage boosting item that is unaffected by either your attack bonus or base attack... sorely needed for Elves, Gnomes, Goblins, and Dwarves who are looking to compete with Humans, Orcs, and Trillings.