You should add a badge for when a user goes over 9000 rep that references spiky hair. Perhaps allow them to wear a spiky hair on their avatar for a day or so to celebrate. That would be good fun.
It would seem that my idea has not been generally well received, and granted maybe the idea of adding a hat went a bit to far and the over 9000 was a bit to localized. However, I think adding anything that would encourage someone to participate on the site is a positive. Maybe a far better approach would be to add some sort of badge every 2k rep or something and allow the community to vote on what they should be. That would have two positives 1) increase participation 2) allow the community to take more ownership in the site.
Further, this is an approach you see all the time in mediums where you earn points for doing things, see achievements on just about any game in existence today.
There are also plenty of other badges that do little/nothing to encourage positive behavior or teach users about the site.
- Popular Question
- Notable Question
- Famous Question
Also as mentioned in comments below, there are badges that reward rep earned