I have a simple solution to this massive problem.
1. Make sure no user gets to post or create thread directly unless he has at least 20 posts. 20 posts will enable comments and 30 posts will enable new threads.
2. Before limit is reached all posts or threads must be approved my mods.
3. If mods find it too difficult then elevate some well known active users here to mods, or better yet create a new status called Approvers or Volunteers if possible. These people need not have full admin/mod rights but the right to approve posts/threads for individual section he/she is responsible for.
Everyone wins, except the spammer.