As another random guy on the internet, I find Wei Dai's comments and posts interesting and important and I don't refrain from upvoting them.
One excuse you can use to give yourself permission to upvote what looks good to you is that even if you're wrong, you'll at least have given increased visibility to a viewpoint that is attractive but needs correcting. I think of my upvotes as not necessarily saying, "I endorse this as correct and the final word on the matter," but rather, "this seems like a good point and if it's wrong I'd like someone to explain why."
As someone who tends towards wanting to provide such explanations, even as the Devil's advocate, I feel that a significant amount of upvotes makes a reply more "dangerous" to attempt to dismantle in terms of the potential for downvotes received. For example: I feel at though your opinion is widely held and there is a significant potential for my current comment to be downvoted. I may be wrong, but I feel as though the perception that my perception is incorrect itself will tend towards a downvoting, even in the presence of such an explanation writ...
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.