The shape of the icon is not what makes it attractive it's the relative rarity. The only time the icon should be visible would be if the mentor queued via mentor queue. The list of registered mentors is a great idea and gets back to the spirit of the system. Move the mount to some other achievement. If there has to be a reward make it a 'gold watch'. Yes I'm well aware that wrist glams get hidden quite often.

Alternatively make the crown a "veteran crown". Give it to anybody who's got Tank, Heals, and DPS to level cap.