As for the spamming; if a new thread that is already in existence and still active is created then the best solution would be to simply report it to mod for the thread to be locked or deleted and the Op of that thread should be directed to the already existing thread. But the issue we are going to experience is that many users would be hesistant to report the thread as they could easily use it to complete their signature weekly quota, and that's why you still see some thread that should have been reported for it to be deleted is still active.
TL;DR if an already existing topic is created click "report to moderators" and report it, as simple as that.
I used to do this back when the gambling section had more redundant threads, but I got discouraged when most of my reports got marked as bad. At that time, they would usually delete these threads, but nowadays, most threads would only get locked or moved to a different board.
The other alternative is to discourage others from posting in these threads because they will be pushed back to the next pages very fast since we have a lot of active threads in the gambling discussion board.