If the rejection feature gets implemented, I suggest considering giving posts that haven't been approved or rejected an extra chance at the queue after 3 days are up. It's not gonna make the queue any easier to deal with, but it will ensure less posts fall through the cracks. These posts should obviously be moved to the front of the queue rather than getting piled on at the bottom. Approvers who use the hide function won't be seeing it again, so it wouldn't bother them.
I also suggest keeping rejections separate from downvotes. There are cases where a picture might have a few flaws and an approver might want to point them out, but it's borderline enough not to warrant the downvote. It would also give more influence to the score metric when an image really doesn't belong.
I like the watch idea.