Marker of good quality would be too far (and biased), as the every growing mass of genuinely hard to salvage closed question certainly outnumbers the interesting ones
But it sure looks to be bimodal. Marker of the really bad, and the so-good-it's-closed
I would guess that this bimodality correlates with one in the personalities of those who become moderators - on the one hand, those who are willing to put a lot of effort into keeping the community relevant, and on the other, those who abhor any perceived irregularity.
On occasion, when I get invitations to participate in moderator elections, I look to see if I recognize any of the candidates. Once or twice, I have looked through the candidates' resumes, and one thing that struck me was that some of them did a lot more down-voting than up-voting. Make of that what you will.
But it sure looks to be bimodal. Marker of the really bad, and the so-good-it's-closed