Perhaps we could measure meaningfulness by the size of the tree of replies and assign karma according to that. That would even solve the post-to-upvote ratio problem.
I just don't know what to do with the downvote-for-disagreement thing. Not everyone regard it as a problem, but I'm not sure I agree.
Maybe Slashdot-style metamoderation...
One measurement to make might be the votes divided by comments.
Let V = votes
Let C = comments
Let IT = 1.0
Let R = V/C
If R > IT then the article is "worth IT"
Let "the paper it's written on" be 0.1.
If R < "the paper it's written on" then it's not worth the paper it's written on (not that it's written on paper, but you get the idea).
But all this is tinkering around the edges, and doesn't feel like it's significant. Perhaps a new model of how a site like this works at all is necessary.
I'm not sure I agree with you on that. The best stories produce a high volume of high-quality discussion. Your proposed algo punishes submissions that generate discussion, which seems to be the opposite of what's desirable.
It's not perfect, but I'm finding it a pretty good predictor.
Additionally, it's very hard to have a high-quality discussion that is also high-volume. Once an article's comments get over several pages long, you can be sure that most commenters are not reading everything before commenting, so you get a lot of similar comments. Sometimes this is valuable (e.g. "Ask HN"), but most of the time it just worsens the signal-to-noise ratio.
I made it for myself. I'm sure it misses some good stuff, but what does make it is almost always top-notch.
Note: there's a hidden span after the links with the score if you're curious. I have it hidden because it can be distracting.
Maybe we could get better results by identifying unanswered questions.