I think things work pretty well as they are. I can't see people being more willing to share with the group just because everyone who will read something took two minutes to create an account and log in. There is alot of great info on hear, I know I've learned alot, but somethings just are not meant to the given away.
"Remember, my friend, that knowledge is stronger than memory, and we should not trust the weaker" - Van Helsing
you do it. Dont do a minimum post count. Do a date joined. Ie member for 2weeks or 6 months or whatever you decide. reason being post count will increase folks joining and posting every 5 minutes just to get the post count up.
OR
if you do set it to run with a post count. I would suggest a topic in the scuppers labeled off topic, that was any posts having to do with nonsense can be posted there..