Given the number of spammers (and other 1-posting drive-by's), how about designating certain threads as "fly paper".
Fly paper threads have a high post count, and lots of buzz words, but are essentially useless to anyone who actually bothers to read them.
If someone actually posts on them, they basically haven't read the thread (or indeed the rules).
Posting to a fly-paper thread is apparently "successful", in that the poster actually "sees" a page refresh with their post, but the result isn't in the post database, and nobody else sees it either.