Another thing I've considered is having specific types of flags on comments, and having them have different effects. E.g. there could be a flag for incivility, and if you got enough of those (maybe in proportion to your total number of comments) you'd actually get kicked off the site temporarily.
Old guard would prefer to vote on a "Contributes/Detracts" axis, while new users vote on an "Agree/Disagree" or "Like/Dislike" axis.
Arguments about this erupt in threads, with newer users generally saying, "It's a democracy, this site is what the majority want it to be, and if most of us want it like this, your loss." But such an approach devolves into pop pablum.
I believe most other ideas here would be unnecessary if the meaning of the up/down arrows could be resolved either socially or algorithmically.
The "correct" solution would be to offer a quadrant, with contributes/detracts on one axis, and agree/disagree on the other. But that would require a rewrite.
Instead of a rewrite, I'd experiment with temporarily changing the arrows to say something explicitly supporting well reasoned comments:
17 points by uptown 1 hour ago [ contributes | detracts ] link | parent | flag
Some would undoubtedly still interpret these as a rightness axis like "agree/disagree", so perhaps an even more familiar pair of terms: 17 points by uptown 1 hour ago [ content | spam ] link | parent | flag
However, the term "content" might lead to voting up every valid content remark, so the positive word should be something with more of a value judgment, while still being a word that can apply to points of view with which one disagrees: 17 points by uptown 1 hour ago | interesting* | spam | link | parent | flag
The idea with the vocabulary choice is that a neutral comment would not be clicked on, and "interesting" is directly in the HN charter.I think this type of vocabulary is more in line with the desire to see well reasoned or contributory discussion flourish.
* Mouse over the word "interesting" could tooltip: "This comment made me think."
// This account is ~400 days old, but a prior anonymous account is ~800 days old, giving some perspective on the trend over time.