I have maintained a forum in the past where users literally begged me and my staff for more storage space for their PMs, galery, longer signatures, custom usertitle or fancy usergroup images.
Now I was thinking, why not let your users actually earn those extras and "purchase" them with their "money"? I was thinking of a points system that works a bit like the trophy feature of XenForo.
Users can earn points (money) by posting, by liking content etc etc or simply by staying active.
Earned points can then be used in a store to purchase more storage space, to purchase a custom usertitle, to purchase access to certain sections etc.
Users should also be able to donate points to their friends. Points should also be connected to the warn status of users. If users were warned moderators can either choose to take any amount of points of their liking from them or a pre-defined amount as a punihment.
In my opinion this would increase activity and traffic immensely and what other forum software would be better suited for this than XenForo?
I know there are already similar add-ons available in bd banking and xenShop but I don't know if they work exactly how I described my suggestion of this feature. I doubt it, though.