Also in English (and one of my favorites):
Stein, Klaus, and Claudia Hess. "Does it matter who contributes: a study on Featured Articles in the German Wikipedia." Proceedings of the eighteenth conference on Hypertext and hypermedia. ACM, 2007.
Thus it appears that their German version might meet your requirements:
Stein, Klaus, and Claudia Hess. "Viele Autoren, gute Autoren? Eine Untersuchung ausgezeichneter Artikel in der deutschen Wikipedia." Web 2.0—Eine empirische Bestandsaufnahme. Vieweg+ Teubner, 2008. 107-129.