Hacker News Guidelines

The only one I subtly disagree with is "comments should be substantive". What it discourages I think is comments like "thanks" or other really 'unsubstantive' comments. It's true that maybe it adds noise, and in many cases are maybe supposed to be inferred without explicitly saying. But I think discouraging this slightly leans behaviour towards snark vs not. (If you see comments like "thanks" you're less likely to be snarky than if you see 'substantive' but maybe too harsh critiques in the comments that appear because "cool project!" isn't allowed.)

Personally I like to make it a point to break this rule from time to time to reduce this pattern.

Same. I think it's especially important to thank someone when they might otherwise assume you'll want to pick apart with their response to you, after you've asked them to write it.

One feature I've thought of would be for someone in a conversation thread to know if the other participant upvoted their last comment. Giving someone an upvote and not replying would send a strong positive signal without taking up more space.