I have to agree that the reason I prefer HN so often to other sites (particularly Reddit) is that often, I'm just not looking for humor. Not everything has to have a joke with it. Sometimes I just want to read, or have, a serious conversation. Quora, you mentioned, similarly a great place to read on a wide variety of things; it's like an inquisitive Wikipedia.
I know it's a popular opinion that HN long-ago-reached/is-reaching a threshold in popularity that threatens to ruin it... But before people say that, again, take a look at some of the other sites. Judging relatively? The bar with which to judge a community's seriousness of the topic is lower than you think.
I'd hesitate to call it a "4chanification" of the Internet; I actually still often enjoy 4chan. It's the spreading of the culture epitomized at 4chan shows making people chuckle is often easier than making them think. And easy comedy, while not inherently a bad thing, is obviously the most plentiful. The prevalence of comedy is also easily to notice on YouTube or Twitter. And it's not that I have anything against fun or being funny. I love David Cross, Richard Pryor, 3 Stooges, etc. I just sometimes enjoy having fun in ways that doesn't include humor. There's also fun outside laughter.
This is what makes me less eager to log into an old forum I used to love. Once a thread entitled "you laugh you lose" repeating things I'd long seen on 4chan became required reading to get any other joke in every other thread, it loses something. I don't have that community feeling I used to.
And say what you will about the quality of HN, even considering the fact that a good third of us dream of projects that would probably put another third out of business, by far and large people here are respectful and contributory rather than angry and wry. We may not be as tightly knit as many, especially given our numbers, but we're a community of quality decorum. Despite what much of the Internet seems to think, there's value in that.
A few months back I actually considered making a go at a gaming news site that would function like HN or Reddit. The idea being to drive high minded people and experts to have serious and civil discussions. It's not only a love of mine, there's a large number of game developers that blog, tweet, and in general communicate with fans. I figure if you can hook a few, you're good. Of course, I dropped that during a rough patch. Things are looking better now...