If you want to ignore the majority of these posters, I would suggest
DannyHamilton's ignore list. While it does sometimes block posters with constructive posts, it is a fairly good compromise to avoid seeing spam.
Danny actually has a whitelist of people who wear paid signatures that do not post complete garbage. This pretty much addresses the issue of not being able to view constructive posts.
I have noticed that since
this crackdown in the off topic section was implemented, that more and more useless threads who sole purpose is to allow signature spammers and account farmers to make a bunch of useless posts has significantly increased in the bitcoin discussion section. There are probably at least 5 or 6 threads on the first page of bitcoin discussion at any given time that most likely have nothing but useless posts in them.