You said “encouraging collaboration between different parts of an organization can have very real benefits.” Here I think your wiki will not only help citizens but people working inside as well.
Taking on another job also helps to see what is done, where the problems are and who is asking for help.
Lastly – its not my idea. The Japonese bring everyone together when they develop a product. What is it, how do we make it, where do we get the parts, how do we tes quality, how much to charge, etc. I believe Mr. Demming who was tossed out by the car company GM took his ideas to Japan in the 1950’s and look at the change it made!
I hope your wiki is not only a source of past informatioin but a source of collaboration.