The truth will boggle your mind: it's not this place that's changed, it's YOU.
When you were a starry eyed noob, you looked upon every thread here as something you'd never been exposed to before. Jokes were new, people were new, everything was new and fun and exciting. The longer you spent, the more you figured out that there's a natural pattern of discussion to the BBS. People made threads that repeated concepts just the same when you were here for the first time, it's just that you had no idea because you were new.
You're gonna go through your "man I'm sick of this place" phase, probably do other things for several months or years. But eventually, you'll probably come back. Because you'll realize that the userbase has turned over enough that things are new and fun again. You'll be further removed from memories of old threads you've participated in, so you won't happen to catch as many repeated discussions.
Really, there's nothing you can do by telling everyone else to do something about it. I wrote a thread that addresses this exact same whining almost three full years ago now. It hinged on the premise that all any poster can do to change the way things are done around here is to lead by example. Make awesome and original threads, be hilarious, be super interesting, whatever. The less prominent posters will see that example and follow it.
Noobs are always going to be ignorant about the way things are done. Mods are never going to be able to catch every thread that sucks, regulars are always going to be slightly jaded about the amount of time they continue to spend here. Nothing's changed and nothing really will.