First, I'm still on the fence in regards to the quality of discussion here. I think there's a tendency for familiarity to breed contempt (the more familiar you become with HN, the more aware you are of things like mean discussions, and the more rose-colored your glasses will be when considering what it was like "before"). There have been a few attempts to objectively measure any degradation of the site, and so far they haven't found anything conclusive, as far as I know. So, it might not be as bad as you think.
Second, you start out with a really general point, but then halfway-through fall mostly into a single example. If that's the example that got you thinking about this, then you've let yourself turn a wasted moment reading a pointless comment into quite a large waste of your time. The friendliest way I can think of to respond to that is that it is a very silly thing to do. :-)
What are you even doing online, anyway? I mean, for me, at least, being online makes me feel pretty miserable afterward, especially compared to anything else I could be doing. I'll look at my threads page sometimes and the older my most recent comment is, the happier I am with myself. That means I've been spending time on better things -- and anything other than commenting on a website is a better thing. I don't want to chase you off, but at the same time, sometimes I sit back and think about all the time wasted worldwide since the invention of the online forum, and how little real positive impact there has been from all of that, and it kinda bums me out. I must've blown entire months on Slashdot way back when, and all I remember from that now is ... uhm ... Hellmouth? ... and ... hmm. I forget the second thing. I am literally a happier, better person, for every moment that I'm not online.
Thirdly, although your intentions are good, you are criticizing behavior which leads naturally from the design of the site. How much thoughtful discussion is really possible on a site like this one, where most threads come and go after just a few hours, never to be read again? Hell, I wrote about this 9 months ago (http://robsheldon.com/conversations-online), submitted it to HN (http://news.ycombinator.com/item?id=2423975), where it got a little bit of discussion, and then that was it.
Forums like this one are designed to be topical, not thoughtful. With the invention of internet points -- yay, karma, and all that other nonsense -- people have had more incentive than ever to quickly bang out a single-line joke, get a point for every chuckle, and move on. (One of the things which has gotten me the most yummy internet points was a joke -- http://news.ycombinator.com/item?id=1102126 -- and, although it was pretty funny, it wasn't nearly as meaningful to me as, say, http://news.ycombinator.com/item?id=3132576).
HN is not a good place for thoughtful, meaningful discussion. It maybe says it wants to be, but the most important things about its design say otherwise. So at some point, you have to ask yourself, "What am I doing here?"
...Every time that I look at this comment for the next few days, I will be ashamed of myself, because I will know that I wasted 15 minutes writing a thing which would be read by a few people for a few hours and then never again, and I could have played a good game of Go instead.