First off, let me say that I am not against deleting questions. I have done a fair bit of it in the past.
However, I think that when the same three or four people account for 80% of the deleted questions that I've seen recently, something might be amiss. (Names aren't important, but if you have 10k you can check the recently deleted list and see what I mean.)
Thing is, it's much easier for a borderline question (or a duplicate) to be deleted than undeleted, simply because you won't randomly run across it once it's deleted. And the consequences of overzealous deletion are worse than the consequences of overzealous closing, since information is being destroyed for the vast majority of users.
So I propose rate-limiting the deletion process like every other process on the site; my initial suggestion is 6 votes per day, but the exact number isn't important right now.