I know that there are restriction on signature but, newbie sometimes keep spamming must by replying on ever thread. Some spammers will be banned and some will not be. This feature can filter out many spammers and allow only those who are here to learn, explore
I think Bitcointalk already have this feature of deleting the irrelevant or spam posts and also banning the users who do Spamming.
One thing they mentioned was the restriction for the new users. It was mentioned that the new users cannot comment until they have some credibility as he/she will be treated as a learner in that time period.
I don't think this is the right way of treating a new user. New users are here to learn new things and ask doubts/queries they have. If they are restricted to do that then how they can learn? As they start commenting and posting the queries, they can increase their account credibility by gaining merits and becoming a Jr. Member, Member and so on.