I get your point but, who gets to decide if a thread is boring or not? What gets stuff on front page is the collective opinion of the community. Saying that something on front page is boring is merely a personal opinion.

Lack of the ability to downvote definitely cripples the way to represent the opinion of the community about a specific thread. Considering that, your argument makes sense but my point is, flagging the thread will make absolutely no difference as long as there are a significant number of people who show interest in it.