I think it's a good idea to deactivate all accounts that haven't been used for say 6 months since we know some of the banned users have some old IDs they can reactivate. In fact I see from a quick google search that it was someone called Legend-Lives who suggested this idea ealier today on another forum! But I doubt it will make a huge difference.
Restricting new users to say 5 postings in the first day may frustrate those who want to dominate the scene for a day if they are impatient and want to act immediately.
But of course if they are patient they could easily get round it. They just start up an inoccuous thread such as "who has tried those new biscuits " or "what is the name of that cheese..". and then wait to punce a day or two later.
I'm guilty of responding too often to these posters and I'll try to resist the temptation from now on, and perhaps others will too, because if no-one responds they will probably get bored and leave.