So far I'm up to New Game+++. It's been pretty fun, a nice little distraction when I just need something calming.
Just a note, on one of my runs I tried to do a sort of challenge run with just one of each "friend", and just stack up lots of hats. It started getting buggy after a bit, and one of the little helpers (the rock thrower, in my case) started having trouble with moving left and right really fast in place, preventing them from picking up any more hats or throwing rocks. A quick reset fixed it, though.
That said, I did notice that the hats do not continue to speed up rock throwers, and there is no benefit to increasing the damage they deal. It's not like you get extra items popping out, so it kinda killed the whole challenge run idea.
Anyways, just thought it might be good to let you know about the weirdness I found by pushing the limits in strange ways on repeat runs. XD