Having a table laid out like that, easily available from the front page ("Site Map"?) would be a great start, especially if it can self-update (is that even possible?)

Click to expand...

There is a MW extension that allows the subcategories listed on a category page to be expandable, to any depth (IIRC). Wikipedia uses it. So it should be technically possible to create something like that. A "category browser" nav widget in the sidebar would be very useful. Maybe I'll have to look around to see if there is already an extension for that.