I would also clean up the logs a bit.
They are huge so it may be easier to ftp to the site and delete the files in the folder.
As far as post count promotion. goes try:
https://www.ubbwiki.com/wiki/view/82/groups.html
You already have a flood check so add say 10 posts to promote them.to user.
If you make it to small a number then a spammer could just post several posts back to back and be promoted.

Blue Man Group
There is no such thing as stupid questions. Just stupid answers