I do like the idea of a paid membership (copper) to allow users to "skip" the process of accumulating activity points to achieve a certain ranking status. If someone buys a copper membership, at the very least, it shows they have a genuine interest in participating in conversations.
I think it shows they have a genuine interest in spamming the boards to earn revenue from their sigs.
Well having a copper membership does not provide for any protection against getting banned. If you pay $40 (+ a $20 tx fee) for a copper membership, then you will need to earn at least $60 (plus the cost of spending your earnings) just to break even, so users have an incentive to not engage in activity that would result in them getting banned.