Minimum comment length of ~50 words.
This would A) get rid of casual snideyness, as those sorts of people wouldn't put in the effort to formulate a longer post; B) discourage crowd-pleasing one liners, which while enjoyable have a long term negative effect; C) still allow jokes, they'd just have to be asides to actual substance; D) encourage longer, better thought-out posts in general, and backing up of claims.
I can spend all day writing a post that has no substance, garners upvotes (in today's HN climate) and is as long as the day, but that doesn't make it good, or worthwhile.
Many of my short remarks are actually more to the point, or are asking a relevant question, or are politely correcting errors. It takes considerably fewer words to do this sort of thing than it does to be mean, while trying not to look like it.
To add to that, lionhearted posted a comment about inevitable site decline because of open membership and equally weighted voting. What if only accounts over 1 year could vote (or diminish their vote weight)?
Wouldn't instituting a min. length requirement and taking away new user voting improve the problem significantly?
However, I suppose you could argue that valuable content would be blocked to some extent, it a knowledgeable contributor was put off because s/he didn't have time for a longer comment. Still, 50 words isn't much, or 30, 25... anything above the average sentence length I suppose would start to have the desired effect.
On your other point, I'm thinking that short unwanted quips can rear their ugly head anywhere along threads.
The problem with time wasters is that it's no big deal for them, they're already wasting their time. It's always going to be up to users who care like you, me and others to try to mitigate the exposure of those time wasting comments while not penalizing legitimate contributions by users who care, and that's why I don't think a hard comment length should be implemented.
I just think that it's far too easy to game.
Another big issue with comment quality, of course, is in the general vagueness of it all. Jokes, for example, are almost always discouraged. Almost. On some occasions, it's quite appropriate.
(Or at least, that's what I assume it's like -- I don't know, I've never been invited into any elite prestigious clubs...)
Even if you say "Oh, it's just a time requirement", what are you gonna do if Big Name Smart Person shows up wanting to comment? Surely you're going to let them in. So now you have an elite line and an unwashed line and you're arguing about who should be in the elite line.
This would backfire because many useful comments aren't that long, and therefore people will be forced to pad them, this decreasing the s/n ratio.
For example, my paragraph above has 24 words.