Or turning it around, what are the processes on Wikipedia that inhibit excellence and promote safe mediocrity?
Insistance on content which consists of the canon of accepted knowledge. While we almost sounded the alarm about the subprime mortgage we did not; we just repeated the information that was put forth by "reliable sources" that property values always rise.
Exactly. Two processes that inhibit excellence are NPOV and NOR. Of course, these are in place because they are necessary to achieve "anyone can edit". I don't know how Ayn Rand thought about the creation of works by committee, but it seems pretty clear that "anyone can edit" directly leads to mediocrity.
Interestingly, I found a comment by Erik Moeller on this topic that was made in 2004. The comment was over a statement made by someone else that "Great brilliant works are built by individuals. Groups of people can only create average works."
He ended his post with this comment: "We don't try to trick people. We are all seekers of truth, and we are all united behind that altruistic goal of helping one another to find it. And that, I believe, is true brilliance."
I'm 100% sure that Rand wouldn't have condoned *that* statement. I don't know if Erik still considers himself an altruist, but his efforts in trying to relicense contributions, without the permission of authors, in order to lessen the attribution requirements and serve the greater good, certainly are the work of one.