First, read the PSNA if you haven't already, it features good ideas on documentation and especially process and how to deal with "layer 8" (management, users, whatever is the "real world" for you).
Next step is the wiki. You seem to already have that, good. People here have suggested SemanticWiki, but I'll point you towards Ikiwiki as it has the advantage of (a) being git based so completely decentralised (have a copy of your files on your laptop during a downtime!) and (b) written in perl so you can probably extend it.
Make sure people know where your wiki is and *use* it, so it doesn't become this rotten piece of outdated documentation out there. You have only started to understand how this is going to be a pain: documenting is hard long-term work. there's a (bad) reason why people don't do it effectively: it takes time and dedication.
Next you can consider using dedicated tools for certain things like inventory or issue tracking. We have used Request Tracker with good success. It's a very solid product that does a lot, also in Perl, coincidentally enough. It also has the Asset Tracker plugin to follow inventory, but i haven't personnally used that, although I had good feedback from peers that used it successfully in an heterogeneous environment. An alternative is OCS inventory, which I haven't used either.
So, just bite the bullet: you're going in the right direction. Just consider the right tool for the right job is your next step, i guess.
