Yes, the problem I see here is that if you start deleting threads you could easily get rid of the entire Gambling section, the Bitcoin Discussion section and probably most of the entire forum because posts that are not trash originally, become trash after the first page, as the original question has already been answered but people keep posting replies page after page.
I won't delete threads of actual substance, but you're right, even decent threads where some actual quality discussion
could take place just quickly turn to shit and are swamped with utter drivel by sig spammers who don't care for any meaningful discussion - just hit and run and on to the next thread to churn out a sentence or two. Back in the day you might have got some decent answers to "What does bitcoin mean to you" or "Why do you believe in bitcoin" type threads, now it's just "i can earn sign camp for my daily needs" type bullshit page after page.