What if you made community contribution a limited resource?
Continuing the reddit example. You could limit contribution by three routes:
1) Limiting the number of posts. For example, 3 posts per week, max.
2) Limiting the visibility of posts. The more you post, the less an upvote counts. Effective Upvote Value = 1 / (posts this week)
3) Limiting the visibility of posts based on post quality. The more you post in a week and the lower your per-post average karma, the less an upvote counts. Effective Upvote Value = (per-post average karma) / (posts this week)
Just a thought.
