On reddit, I often collapse long threads of comments if I'm bored of reading them (I have neither the time nor the attention span). It has no bearing on their quality.
Something that I always found a problem was getting "stuck" in the middle of a huge comment chain of irrelevant content, so I made a chrome extension to fix it:
On reddit, I find [personally] most of these threads are never-ending chains of well-trodden memes or loops; this isn't something usually encouraged on Hacker News. If a thread is boring or doesn't pique curiosity it probably isn't too encouraging.
I do that too as far as Reddit, but I agree w/ OP. Reddit-style collapsing is useful for reading & skimming but it doesn't persist across browsing sessions. On the other hand, the 4chan UI will hide a thread and all its updates forever. Sort of like if you could collapse/downvote reddit headlines off the front page. (is there a plugin for that?)
HackerNew (apologies for my inability to present this link elegantly) https://chrome.google.com/webstore/detail/hackernew/lgoghlnd... allows folding and dynamic loading, similar to RES. It also increases the font size slightly by default, which I am embarrassed to admit is rather nice.