My first response is "what a good idea". My second response is "what about funding"? Wikipedia would require many times more employees if this method was adopted. And not just grunts, either. People who have some level of specialization, and therefore, expect bigger checks.
I think a possible compromise might be to have "account validation" of sorts. Add an accreditation option for user accounts on wikipedia. If you can prove you have, say, a degree in economics, maybe you should get more of a say in articles about economics. That's the best "half-way" option I can think of.
Wikipedia is just the obvious comparison, I think this method could be used for lots of user-driven sites.
Still, the SEP is a really cool site, and well maintained. A pretty ingenious solution to a long-standing problem.