Off-topic, but you mentioned the Mage Plate, Darvin. Where is that?
Labyrinth; you must defeat it as all of the T1 classes
The Mage Plate gives you +1 MP, but -5% attack bonus, every time you level up. If you convert the item, both the benefit and penalty goes away. Basically it's the Attack->MP booster prep on steroids. You're not missing much; it's pretty much only viable for pure casters and still doesn't perform well as a prep since the Crystal Ball is its superior by a significant margin. Human hybrids with the HP->Attack booster prep can also make good use of it, but it's generally too much effort to get that combo off the ground.