Rewards are nice, but helping is supposed to be its own reward. After all it is a Volunteer position, and I see no problems with some sort of Volunteer appreciation event; but in-game mounts and such seem a bit much in my opinion.

I joined the program because I honestly wanted to try and be of help to others, not because there was the promise of this or that thing that I can only get if I am a Mentor. My reward is my service.