I don't think a single merit requirement is of any significance, it's too easy to feed into an alt and bot network. I've mad a number of suggestions in the past, and some of them are.
- Newby thread starting restricted to an intro and an account recovery board. Newbies and juniors restricted to beginners and associated boards.
- Merits associated with posts deleted by a mod, or by the poster should be removed.
- No merits for trading, bounty, ICO or similar posts.
I think there were a load more, but that will do for the moment.

I think a single merit requirement would be quite good. It means that multiple bots can probably get detected by simply tracking their merit sources using Ddmrddmr s tools. Patterns would be easy to identify.
It might take some time but eventually their sources for merits will be exhausted and it will become more difficult for them.