I think a system like how Slashdot moderation works. You get X points to rate issues or comments based on how many points you have. Comments get a value -2 to 5. Default view only shows 0 to 5. You really only focus your efforts on removing things with a negative rating.

I remember it working surprisingly well, especially browsing at 1 or higher, and I've never understood why no one has replicated it. 'Karma' systems must get better engagement.