Unfortunately, I don't have a good way to tie Editor permission to post count that I can see. The whole point of wiki is to be an open discussion. mahuti is correct in that wiki has rollback and diff capability, so it will be up to the editing community to police itself. The global moderators and admins on the forum have the ability to protect or delete pages as well, so come get one of them if there is a serious issue.
We can also block stuff by IP, and I can require that anonymous users cannot edit. Thus, they would have to register on the forum to edit the pages.