I think I was involved in exposing both cases that the OP refers to.
As I assumed, writing a large number of posts in a short time is not often aimed at rank upgrades, so I would suggest implementing a solution similar to the one on Bitcointalk at least when it comes to promotion by rank.
In fact, there the activity (necessary for rank upgrade) is calculated every two weeks. And the maximum you can improve the activity is 14 points. Even if you write 100 posts for that period.
I don't know how feasible it is to do something like that here, it's a matter of administration and a question for the admin, but certainly, restrictions in that sense would discourage excessive spam.