0 - Ability to comment on threads
50 - Ability to upvote comments
500 - Ability to downvote comments
1000 - Ability to submit articles/stories
2000 - Ability to downvote articles/stories
etc. While this may reduce the number of incoming stories, perhaps there could be a way for power users to sponsor stories submitted by those who aren't able to submit them to the feed themselves. The more I think about it, the more I like this approach - create a queue of "pending stories" that anyone can submit to, but only those who have sufficient experience on the site can approve them (or remove them from the queue).
For those who say that I'd be pandering to myself here, note that I'm at 620 points right now - with this proposition I'd be reducing my current abilities. However I think that it's a small price to pay to improve the quality of submissions.
This approach may work if there is additional points given by the system to the upvoter (or downvoter) if there is significant number of other users doing the same thing as that upvoter (or downvoter) too, which means his/her action is indeed valid and objective.
Users would then be more willing to vote, with the hope that other users will do the same thing as him/her too, and reap more points than what he/she spent for upvoting/downvoting. This enforces more thinking and evaluation of comments or stories before even upvoting or downvoting them.