Post count and staring at these forums does nothing to solve the bot or spammer problem if not only exacerbates it.
How do you come to this conclusion?
Put a 24 hour or longer membership requirement and leave it at that.
If I were a spammer I'd just sign up 100 accounts and wait 24 hours. You've just made life as a spammer much easier.
Have them graduate in levels, after 24 hours allow to post in the general forums, after 1 week all greater access.
Do it in waves as far as access level.
This doesn't work because any spammer is going to automate signup and just wait, go away and do a weeks worth of spamming and come back to hundreds of new spam accounts.
You'll need to do better than this.