Amulets are just far too important an item slot to be wasting on something purely cosmetic like a permanent Transformation.
Mastery Amulets just open such a wide window of possibility for a Wizard, and the new Zafarian Amulets give good HP and very useful, non-trainable Spells. It would be a tough choice for me between looking like a Mander and having a Wizard that isn't totally underpowered.
So instead, I propose we have the option to purchase Permanent Transformations. Sounds easy enough, right? They'd have to be Crowns Only and Over 9,000 or so, maybe. The only way to get them off would be to remove them permanently, so it would be a tough choice for a Wizard to never see what their clothes look like anymore.