Wikilove the tool in particular, or barnstars/appreciation in general?

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0034358
 found productive people, gave half of them barnstars, and looked to
see what happened. - "receiving a barnstar increases productivity by
60% and makes contributors six times more likely to receive additional
barnstars from other community members"

https://meta.wikimedia.org/wiki/Editor_Survey_2011/Wikipedia_Community
had a general question about appreciation through barnstars etc, but
"do you like people
saying nice things" is not the most rigorous study ;-)