So what about competition?
Since many gamers are very competitive, I was thinking, why not do some reward system for tittles or something. For example 10 post your get a tittle added to your name, 100 post you get another tittle. Or even a level system with exp for doing things that require members to log in and be active to gain experience points. You have the Arcade working, so you can even branch off of that even more.
Life is an art, your the artist, and the best paintings are ones filled with passion and emotions.