But that would have the unintended side-effect of making the site much more attractive to spammers because they'd be almost guaranteed some homepage exposure.

Feature a random article selected from new articles submitted by users with at least 10 points?

Feature a random article selected from a probability distribution based on user karma.

e.g.

    Alice   - 100
    Bob     - 200
    Charlie - 300
    Dave    - 0

Dave's new article will never get front page exposure. Charlie has a 50% chance, Bob a 33% chance, and Alice a 16% chance.

If you want to modify the probability based on karma points, I would suggest giving larger probability to those users with fewer points, as those with more points (ostensibly) would already get more attention given to their submissions anyway.

Dave won't get anywhere with either this scheme or the one I proposed, at least not immediately. But that's the idea: it will be a little bit harder for Dave to gain traction, but it will demonstrate that he's not a spammer, which should be a reasonable price to pay for ensuring the site isn't overrun with garbage (any more than some claim it already is).

That wouldn't work either, it would simply cause a karma feedback loop.

Worse things have happened. You could easily cap the "considered" karma at like 500. Or some value that is a function of the total karma in the system.

EDIT: or cap the "considered" karma at the median for all users.

Would it really?

Since the signal:noise ratio on the /new page is pretty darn good right now, I don't think that featuring one of the new submissions on the homepage would change that much.

Also: this proposal would only lead to more impressions for the spammer if the homepage received more than 30x the traffic of the new submissions page. That may be the case, but how would a spammer know that?

Try looking at the newpage with 'showdead' set to 'on'.

Right now I count 8 'dead' links, but it's not rare at all (especially when it's quiet) to see 15 or more.