Well, ROR project is running into similar problems with managing documentation:
http://wiki.rubyonrails.org/rails/pages/ManualDiscussion
It seems to me that the solution is not an exclusive choice, but to manage the available resources well.
Topics that change fast, fragment by system etc (such as install docs) should move to the wiki, and docbook be used for more structured documents, where presentation formats can be changed on the fly...
