I see good posters being permabanned because of this, while the actual scammers/super spammers are all over the place.

The main reason this doesn't make sense is that someone with an established Hero+ account that did something wrong years ago is NOT going to risk doing anything stupid ever again and has probably learned enough stuff to produce decent posts. Banning old members from stuff done years ago is an obvious net loss. Someone that was bright enough to come here years ago when bitcoin wasn't mainstream has learned and probably has good things to offer. Everyone coming in now are just jumping on the bandwaggon.
I wouldn't even bother with signature permabans. Who cares if they are producing good content? just ban the people that are cluttering the forum with nonsense, as readers we don't give a toss if someone copy-pasted two lines 3 years ago when they were noobs if they have been doing it right since then.