I have a few thoughts.
Thinking financially here: while I'm not aware of studies, the rise of Wikipedia coincided with the demise of Encarta. Also, I think that you'd want to take into consideration the impacts that Wikipedia has had via its appearance in Google search results and in Google's information summary panels; I'm sure that Google has reaped substantial financial benefits from Wikipedia. (This is a mixed blessing.) You might consider making an estimate of how many millions of dollars university and school libraries have saved by not purchasing proprietary encyclopedias.
You might consult with WikiProject Medicine and WPMF to learn about the public health impacts of their efforts in content development and translation efforts, which they seem to think have been substantial in the developing world.
I believe that the education folks in WMF and WEF have done some analyses of how Wikipedia assignments have may have yielded improved student engagement with material than traditional course assignments.