I think the real problem with the mentor system is exclusivity. I believe the answer is to change the icon from a crown to something a little more humble, and let any one use it without any sort of requirement.

What is the intended purpose of wearing the crown? To let other players know that you would welcome questions and like the be helpful.

The 'exclusivity' of the crown seems to makes a lot of people bitter; "He is wearing a crown but he stood in bad. I didn't stand in bad even though I don't have a crown."

Exclusivity and the icon itself are responsible for turning the icon into a point of pride and source of resentment. If we take away those things then people who don't want to be helpful will be less likely to chose to wear it, and those that don't wear it wont resent it.

Will people who shouldn't be giving advice give advice under such a system? Yes. But it seems a lot of people believe that the case with the current system, so I don't see this point as a loss.