I thought it was at 100, then 200, then 400 karma, but still no dice... Does anyone know the threshold when you get it?
If you are frustrated by the quality of the front page on Hacker News, one thing you can do about that is emphasize the positive by visiting the new page
http://news.ycombinator.com/newest
and upvoting the stories that are good. I often see good stories on the new page that never make it to the front page. There is a lot of good stuff submitted every day on HN. Improving the signal:noise ratio here means improving both sides of the ratio, by flagging bad submissions (submissions that violate the guidelines, including submissions of on-topic content from lousy sources) and upvoting good submissions.
Voting rings have been (are?) a problem for HN, and I suspect a reward system for people who are active on [new] will be open to abuse from voting rings. But I don't know - maybe there's some interesting science / math in online voting and reputation systems.
Closest you get is flag which happens at around 20 karma and reduces the staying power of a post.
(Not saying you're wrong; you're just not universally right.)