I disagree, if the the count is higher, then they NEED to spam MORE to reach the goal.
I'd actually agree with xntrik. It's more likely that people who would spam in the first place would be discouraged by the 5000 post requirement. I think we'd have more spam by newer members if it were 2000 posts. They'd see the goal as easier to reach and just go for it. It's much easier to spam 2000 posts than 5000.