Yes, it would, true. Wouldn't the newbies then be quite singled out though? People would know who to get annoyed at.
Hmm. That's like saying John Howard's older than Kevin Rudd therefore he's better than him. I don't think it's the date joined that makes people "better" than others. I'm not exactly comfortable with this type of ranking.
The same is true of the current system of post counts, for the most part. The great advantage of the date joined would be that, as Bee said, you can't change this date. There's no incentive to spam.
Having said that, it won't stop people spamming. People post because they want to, not just to reach some magic number, even if this is true of one or two people. Visi will openly say "I want to reach x by the end of the month" but someone like Kelch doesn't, she just posts because she feels she has something to say. Nothing will stop that, and I don't think it should.
By the way, I'm moving this thread to the Website board. It really belongs there along with 10,000.