As I see it there (1) are numerous users that would like to contribute something back to CEGUI. (2) There are many who need more or better tutorials and examples. And (3) there are many who don't know what or how to contribute back, especially given simply the vague request "please help us with updating the wiki". In my experience, the more specific requests one makes the more people will actually get on it and faster.
So my suggestion is that we make a wish list for pages and topics that should be made, expanded updated or fixed. A very concrete list with quite specific requests. And post it on a front page, or a stickied top-level thread named "List of things we need help with", "Contributions you can do" or something similar. It could/should be a wiki article too, perhaps on the wiki front page, but it should also be mirrored or at least linked to from the forum, and then from the most prominently visible position possible.
This list should be updated when questions like the one in the above thread comes, or whenever we see the need for some elucidation or improvement on any topic. While it might be understandably difficult for the CEGUI developers and representatives to find the time to write or improve entire articles or the documentation (which is why the call for help has gone out in the first place), it would be very fast to instead simply update the wish list, and it would help would-be contributors toward something concrete to actually help with.
In sum, this is a very simple and low-overhead suggestion that has the change of high return for very low risk. So let's make this list and sticky the thread already!
It also needs to be populated with a few selected items for people to help with.