I’ve seen a lot of things that criticize wikipedia for not having a set of experts running things, and I think a lot of the criticism is misplaced.
First of all, the same sorts of mechanisms that keep “non-experts” out are the same sorts of mechanisms that keep “experts” out. I happen to have a Ph.D. in astrophysics, and if I want to edit a wikipedia article, I just do it. If I have to write a resume, and prove that I’m an expert with something other than my edits, it’s just a waste of my time.
Second, expertise is *extremely* situational. I have a Ph.D. in astrophysics, but an eager high school student that finished reading an article in Scientific American on something that isn’t something I’m actively researching, just plain knows more about the subject than I do. This is an important fact. It so happens that I know an Nobel laureate, and I’ve been in situations where I’ve explained something to him because it was in a field that was in my area of expertise (numerical hydrodynamics) that wasn’t in his. And if you had an undergraduate or first year graduate student in the room who just finished reading some articles in the Astrophysical Journal, that person has more expertise in the area than either of us, and we’ll both be listening to them.