If little numbers are all that motivates contribution, I don't think the motivations lost are or were rational.
I've written more in this single comment section in a few hours than I have in my entire experience on LessWrong outside of this topic. If I were looking for upvotes, I would not act in nearly the same manner or with the same motivation for quality of reasoning. Really, if not for this topic, I would sacrifice principles and reasoning I consider rational for the sake of blending in and seeming more acceptable in the eyes of the voters for the express purpose of getting to 20 karma points in case I decide I have a purpose posting something at the discussion level that I would expect to be immediately downvoted on. If not for this discussion, I'd be here solely to blend in until I have something nasty to say loudly.
As cold as it sounds, no, I wouldn't consider it a loss. It really is a Boolean for me, which I feel isn't giving you the proper feedback your argument deserves, but the individual contributors to LessWrong either have the potential to seriously address and rationally discuss this issue or else there will be a stasis of extremely unoptimal discussion practices that carries no value to me (beyond what amounts to advertising).
Every now and then, I write an LW comment on some topic and feel that the contents of my comment pretty much settles the issue decisively. Instead, the comment seems to get ignored entirely - it either gets very few votes or none, nobody responds to it, and the discussion generally continues as if it had never been posted.
Similarly, every now and then I see somebody else make a post or comment that they clearly feel is decisive, but which doesn't seem very interesting to me. Either it seems to be saying something obvious, or I don't get its connection to the topic at hand in the first place.
This seems like it would be about inferential distance: either the writer doesn't know the things that make the reader experience the comment as uninteresting, or the reader doesn't know the things that make the writer experience the comment as interesting. So there's inferential silence - a sufficiently long inferential distance that a claim doesn't provoke even objections, just uncomprehending or indifferent silence.
But "explain your reasoning in more detail" doesn't seem like it would help with the issue. For one, we often don't know beforehand when people don't share our assumptions. Also, some of the comments or posts that seem to encounter this kind of a fate are already relatively long. For example, Wei Dai wondered why MIRI-affiliated people don't often respond to his posts that raise criticisms, and I essentially replied that I found the content of his post relatively obvious so didn't have much to say.
Perhaps people could more often explicitly comment if they notice that something that a poster seems to consider a big thing doesn't seem very interesting or meaningful to them, and briefly explain why? Even a sentence or two might be helpful for the original poster.