The MediaWiki way is workable, but with manual maintenance of namespace prefixes or categories required, I have a bad feeling as the target users do not have a technical background on the whole.
A simple approach of "be in the right place" and "click new page" to get an implicit hierarchy is probably what they are after, based on an initial chat with them.
I find http://www.mediawiki.org/wiki/Extension:CreateArticle quite useful. Users get an input box for creating new pages which takes care of some naming conventions, e.g. namespace. And you can easily add a template for the new page together with intstructions on what to fill in where.