I don't buy the idea of having to create a new gambling thread for each season. It doesn't really change much of the outcome as, the game remains the game and users that frequent the gambling boards knows better to check out the last page to be updated or current on the on going discussions. A new season coming with a new thread doesn't change that.
The idea shouldn't be about creating new threads just because a new season has started. The idea is to create those threads as self-moderated so that spam and low-value content can be easily deleted by the thread starter. I agree with you that a new thread doesn't mean that the posts in it are good. They can all be awful. The new Champions League thread, for example, is self-moderated. To be fair, the old one was as well.
I like to post in the Serie A thread because I am interested in calcio. It qualifies as a spam megathread. I wouldn't mind someone creating a new one and making it self-moderated if it would get rid of some of the posts where people are just reporting the goal scorers in a match and the team position in the standings.