Not bad, but abuse can also be avoided by raising the merit requirement. Theymos suggested up to 5, but it could be even up to 10, and then change member requirement to 20 or 50.
Massive spamming is created at lower ranks, so its sensible to make requirements tougher for them.
Since the introduction of merit system, good posters (not exceptional ones) are taking longer to rank up than before, but juniors can keep spamming and they are only required one merit. Until recently they werent even required that. I think it is better to make the 1 merit requirement a tougher one.
I'm not saying yours is a bad idea. Both steps can be taken.