Sometimes, I notice that a new account pop up every few days and suddenly become too much active. Once they rank up, they slowly left the thread.
Sounds like someone farming an alt account.
You see the activity because we all are in one thread. But, I don't know if we will see that much activity if we get a local board. But, it's also true that a lot of good posts get buried easily because we are in a single thread.
I don't see how getting your local board would decrease your activity. Sure, posts would be spread acorss many topics but that would also enable the more quality (and lenghtier) discussions which would then increase your overall activity. Just take a look at the Nigerian local board and how much their numbers went up since they got their own local board.