osirisjem, you are correct, there is no Audi A4 'Home Page'.
This was a design decision. We could have had a page with all the content together, like the main page, or instead the content segregated by type. We did some in-house usability tests, and felt that everything bunched together was a little bit cluttered (for instance the home page is leaving out requests, and limiting the number of pictures and videos, etc).
Currently the section 'Articles, Reviews & Links', contains 'Local Wiki Articles', Links uploaded by visitors to luxurywiki.com, as well as links harvested by the Arcane Engine (auto-content).
Initially, when we first started designing the website, we had what you suggested, and slowly it evolved into what you see today.
Regarding the wiki, you can use Arcane Engine and have a more standard wiki installation, with the wiki home page, etc. In this specific case, we felt that the user was going to be more interested in the content rather than accessing the wiki itself.
So, if you go to a page in the wiki, it will have the same look and feel (skin, menu on the top, navigation bar, etc) as if you were in the forums.
vbWiki is definitely working behind the scenes providing single sign-on, and what not.
Currently we are still debating whether to have the Audi A4 Home Page or not. But most likely it would not be the wiki home page.
As you mention, the site is still in flux, we are now conducting external testing, and we will be adjusting the site depending on what we find and the suggestions and observations made to us, such as these you posted in this thread.
Thanks.