Conversely, the impetus to make the basic concept possible might increase if someone made a compelling case for what value it would provide.

Incidentally, I'm not suggesting that people should upvote/downvote based on "interesting" rather than "true".

I'm suggesting people should upvote/downvote based on "want more like this."

That means if I see a true comment, and I want to see more true comments, I upvote it because it's true.
If I see a well-written comment, and I want to see more well-written comments, I upvote it because it's well-written.
If I see a rhyming comment, and I want to see more rhyming comments, I upvote it because it rhymes.
Etc.

Being able to tag a vote to indicate what attribute(s) I wanted more or less of would admittedly be clearer in ambiguous cases... I do sometimes find myself staring at a downvote wondering what the reason for it was.

That said, I'm not sure it would actually add much value.