1. They tend to spend more time reading the "new" queue than average, because they spend enough time on the site to exhaust "top" and want to read more.
2. They're more likely than average to be open-minded about controversial stories as well as less tolerant of inane ones. If they spend more time on the site, then it's more to their advantage to promote interesting stuff rather than promote an agenda. It's dumb to piss in your own pond.
Here's what I propose: high-karma users get more voting power over *young* stories, to enable them to police the "new" queue and out-muscle spammers and voting rings. After stories are a few hours old, high-karma users no longer get a boost if they haven't voted on them yet. If high-karma users have already voted on a story when it reaches the aging threshold, the boost goes away for upvotes but not for downvotes. That way:
1. Bad stories never see the light of day, because high-karma users bury them and they stay buried.
2. Controversial stories will make the front page, but they don't stay there long if the rest of the community doesn't like them.
3. Good stories make it to the front page slightly faster.