I vote a very strong NO for this reason:
It will create a much stronger sense of security than actual security. The actual security is essentially non-existent, because it would be based on the assumption that postcount is equivalent to trustworthiness. This is crazy.
Look, I've earned the title "Sr. Member" with the attendant name-changing fun-and-games rights. The active members here have a rough idea of who I am from my ~300 posts, but posts cannot tell you these crucial facts: I am currently serving a life sentence for a burglary gone wrong. Estelore is a serial killer--on the loose. Faerie is not actually a faerie. And Richard is recruiting for a cult with designs to take over the world.
(Esty, Faerie, and Richard, please forgive me, mmkay? I don't really mean these things, I just had to make a point, see...)
There is nothing that would have revealed these things from our posts. Post count is nigh useless in judging the trustworthiness of people, even if people couldn't get around it by just spamming the boards.
To repeat what I said earlier: develop a policy for what you do and don't share. Kids, talk to your parents. It's OK, really. If in doubt, don't. Then stick to your policy. This is hard sometimes. I currently do not share my real name, even though that can be difficult in chat (and even harder in voice chat) when talking about myself.
Also, I encourage the few members under 13: don't reveal information that can be used to contact you off-line: street or mailing addresses, pictures, etc. on any website. Not just for your own safety, but for the legal safety of webmasters.
Finally, respect other's personal information. For example, I know the full name of one of the members who does not reveal that information in forum. I'm not going to share it, or tell you how I found it (other than to say that I was looking for something else at the time), or even tell you which member.
Actually, if you're tempted to ask me at all, you should use this chance to practice self control. If you fail and do ask me, expect me to shun you.
Anyway, sorry to be so dark, but this is important. I oppose post-count limits because they provide very little security and are much more dangerous in the false sense of security they do give.