I'm not sure what privileges the badges would come with but it probably wouldn't be worth the effort and the amount of people abusing it would be minimal and probably compared with how many people there are abusing the merit system as opposed to using it legitimately.
Probably best, if they didn't actually come with any privileges, and were just a visual thing. We know gamification works, as its been implemented in many other industries. I've mentioned about Universities using it in the past for their students. So, it doesn't need to come with an incentive other than the social status of displaying it on your profile.
If theymos is worried about clutter, maybe only allow a certain amount of badges per user to be displayed at one time. Either randomly or selected by the user. Maybe, only display it on their profile page, and not actually within threads.