That section of the forum is lost forever to spam and there isn't much we can do about it since most active spam busters of the forum that have the interest of the forum at heart are bitcoin enthusiast that's why they concentrate more on bitcoin related sections in regards to reporting spam.

You can do the forum a favor by taking it upon yourself to report any spam (worthless post) you find and they'll be deleted. Also if the fee those ANN thread bumping service provider are requesting aren't that huge you can sacrifice some $$ for the forum, hiring their service and wait until you have enough evidence (high number of accounts) then start a thread reporting all the accounts they use for the service and they all will be ban.