Why isn't there an e-mail notification that posts need Approved? Currently the only way is to go to the Approved Post area in the CP but even then you have to manually refresh that area to see any posts that need approved. It's very archaic in nature.
Your Forums > User drop-down menu > Preferences
"Moderator and Administrator Notification Preferences"
for "Notify me when a post needs to be approved in a forum I moderate."
Click "Save Changes"
If you are having problems with new users, maybe do not force your uses in to your customized automated process which is easy to bypass.
As Gizmo wrote above, find moderators who will clear out the trash posts as needed. suspend or ban the violators. When you have moderators who are online often, they can handle violators quickly.
Use the tools already available to you:
• Set up a delay between posts. Maybe 5 minutes or 20 minutes between posts for new accounts -- I dont know your situation.
• Spread out your automated group changes to maybe 100 posts, vs the 5 posts it sounds like you already have.
• Run the post-count-rebuilder weekly if you have a major issue.
But what it all comes down to is that you need moderators to assist.