"In an enterprise environment, where every contributor to the wiki is identifiable, and every change reversible, what value remains in restricting edit rights a priori?"
I stumbled on this on the atlassian site. My group is trying out Jira and the Confluence wiki. This article from an atlassian developer expresses some of the core oversights enterprise wikis face. Rights management, like any security measure, is a balancing act. How much does rights management cost you in terms of lost good and effort spent managing the management? How much benefit do you gain?
My default setting for behind-the-firewall social software is full rights with authentication, with security imposed as needed, and only the amount of security needed to protect from specific probably problems.