If I had a Amulet as a bond object and I wanted to make it into a Amulet of Mighty Fist for the purpose of polymorphing and so on as I understand it according to the feature description, I only need to be the right caster level? "A wizard can add additional magic abilities to his bonded object as if he has the required Item Creation Feats and if he meets the level prerequisites of the feat." So I don't need the spell magic fang?
What the bond gets you is being able to craft it w/o having Craft Wondrous Object (as long as you're CL 3rd). You still need to satisfy the other item prereqs (or pay +5 DC per), such as spells. You still have to pay the full gp cost, too.