I have few ideas, whether they are good its debatable
First of all I would love to have some kind of game jam competition here. Where you winning game is somehow displayed on website for a while as a prize. Maybe have community vote o the winners themselves since there is already similar voting system implemented for sceenshotsaturday. You can check how lundum dare does it under their judging section below on this page http://www.ludumdare.com/compo/rules/. But most likely you guys are aware of that already.
It would be cool to have achievement/trophy system. Let's call them trophy's during this message since I'm more on PlayStation side
The way I imagine it, that there would be new Trophy section somewhere in your profile.
When gaining a Trophy you would get reputation points. The harder is to get it, the more points.
I would do the system so you can get the same trophy's infinite times or 99 times max. Also one given trophy could be only gained once per day (to stop people spamming certain things). The progress of trophy wouldn't reset each day on other hand.
When you would have icon of the trophy in the gained trophy's section it would have number on top of it which would mean how many times that person receive this particular trophy.
Here are some examples of possible trophy's that came to my mind.
Vote for 5 pictures in screenshotsaturday showdown - 1 point
Vote for 10 pictures in screenshotsaturday showdown - 2 points
submit a screenshot to screenshotsaturday showdown - 1 point
submit 5 screenshots to screenshot saturday showdown - 5 points
get your screenshot to Win 10 battles - 1 points
get your screen shot to appear in Image of A Day - 10 points
Post 5 comments - 1 points
Get Voted Up by another members - 3 points
Get Voted Up 5 times by another members - 15 points
Start New Topic - 2 points
Post an Article - 2 points
Win Article Competition - 25 points
Post in 3 different types of forums - 3 points
Make Friends, Add new contact - 1 point
Write a status update - 1 point
//game jam if its going to be on
Win Game Jam Competition - 25 points
Take part in Game Jam Competition - 2 points
Receive rating higher then 8.0 - 5 points (if there is going to be rating system for games when they are judged)
It would be also cool to be able to link your Linked in with GameDev somehow
Hope this was any useful