A partial solution (well, not "solution", that seems too strong; maybe "medicine"?) would be to remove the post from the queue as soon as someone starts editing it. That would at least prevent those moments of sheer frustration, where you finally finish injecting some sense into an atrocity committed against English grammar, only to find that someone has pulled the rug from under your feet and taken your credit without so much as making a token effort. (If the edit is abandoned, then naturally the post goes back in the queue.)
The other part might be to go ahead and count all review-type actions, even if they're on posts someone else has already reviewed;go ahead and count all review-type actions, even if they're on posts someone else has already reviewed; heck, even if they originated from someplace other than the queue. Naturally, the badge limits would have to be greatly increased. Also, I don't think votes should count as review-type actions: I'd limit it to edits, flags, and comments.