Of course I have a problem with people who have a low post count, especially 141 for some reason.
Well... okay, so the question becomes one of understanding what you want as a standard. Quantity doesn't equal quality; I'm sure that everyone would agree with that. Time has the same problem... you could be around for a couple of years, but not necessarily be very "vocal" or post a lot. But what constitutes quality?
Is it participation? Is it having a good idea? Is it helping others? What about just having a point of view that may or may not influence others? It it presenting facts, or presenting opinion?
On time, do you have to have registered before the contest? How long before?
If the purpose of the contests is to increase interest in the forum (and presumably, increase participation as well) then it seems to be accomplishing that. Will everyone who comes along meet your criteria for quality? Of course not -- but whether they do or not, the purpose is satisfied.
I don't think Dave really wanted to create an "old boys club" or private forum, though he does have the supporters' forum and that would be just that -- a private forum. If you want a lower signal to noise ratio, that would be the place for it.
George Carlin did a bit on a particular priest that wrote a letter to the FCC about something he heard on the radio that he didn't like. His take: there's two knobs on the radio; you can chance the station, or turn it off, but limiting speech because you didn't like what you heard (or in this case, saw) isn't appropriate.
Before you get annoyed -- I'm not at all suggesting that you're trying to limit speech here. What I am suggesting is that you could take a different point of view, which would be to work to raise the quality of the posts by leading by example. It's easy to complain -- it can be harder to do something about it, but it's also a lot more satisfying.
If everyone that's finding themselves annoyed by the new members were to simply respond only to those things that interested them, and ignore those things that didn't, the forum would naturally clean itself up over time. People do tend to follow examples; just set a good one, and stick to it, and the end result will be positive. There will be something for everyone, and nearly everyone will benefit from it.
Just my humble opinion. Your mileage may vary. No warranty is expressed, or implied.