I think I see why the information about MediaWiki is less-than-ideally organized: The people who are really interested in documenting things (like you) don't necessarily have much knowledge of or experience with the software, and the people who really know a lot about it (like Rob Church) would rather be working on the software than writing documentation for it. If you really want to change this, then you're going to have to unite the two parts, either by learning enough about MediaWiki to document all the things you want to document, or by getting the people who really know the software well to help you. Judging by the responses to your emails, it doesn't seem like those people are going to jump forth and help you along every step of the way, so I'd suggest you start poring through every bit of documentation you can find, whether on Wikipedia, meta.wikimedia.org, mediawiki.org, the software files (/includes/DefaultSettings.php has a lot of neat stuff), third party how-tos (there seem to be all sorts of articles scattered through the web on various MediaWiki subjects, if you do a Google search), existing MediaWiki implementations, and anywhere else you can think of. I've been running a wiki for a year now (with some previous experience as an end-user), and I think I have a pretty good grasp of most of the visible concepts of the software; I don't know nearly as much as I'd like about all the code and whirring gears that make everything work, but you don't necessarily need to know all about that to document things as a sysadmin.
I've avoided this thread, but I think you bring up a very good point here, and I'd like to say one thing and then continue to try to ignore this thread.
Peter... If you want MediaWiki documented to the point you find acceptable, why don't you hire someone with the available knowledge to do so? Complaining to volunteers about their documentation not being good enough is rediculous. Do you go to a soup kitchen, and complain that their soup isn't the quality of a four star restaurant?
We understand that our documentation isn't up to par. We try to document as well as possible, but we have development work to do, and most of us have other jobs as well. If you want better work out of us, motivate us with money. You'll be helping yourself, and providing help back to the community. Either way, it would be far better than trolling this thread, and wasting our time.
If you want to hire someone to do proper documentation, please start a new thread offering to hire a knowledgable person with technical writing skills.
V/r,
Ryan Lane