I have mixed feelings about sub-forums for each as model. It appears the software the BB is built on allows only for a hierarchical structure and such a structure inherently doesn't lend itself to efficiently cover topics that fall into more than one category (e.g. parts or problems that are common on more than one model). Furthermore there is the problem that newbies sometimes post in the wrong forum and/or that threads change the topic. I believe correcting such issues by moving and splitting threads would be more than a full-time job and would require significant knowledge about Alfas, Alfa history and specific car models -- more than can be expected from the admins. In addition, I don't think there's an easy solution to the fact that some people use AlfaBB to chat and others use it as Wikipedia.
Furthermore, I think AlfaBB is a bit of a general purpose web site that complements some of the excellent model specific web sites on the Internet (for example, Bruce Taylor's Alfa Montreal
site, Wille's Spider Veloce
site come to mind -- I'm sure there are many others).
Last but not least, the course hierarchy helped me stumble across interesting topics that I would not have thought out intentionally (kind of like browsing through a magazine) and that, in my mind, undoubtedly would have been buried in a deeper hierarchy.
With respect to searching, I have given up on AlfaBB search and use Google instead. I use either "search terms site:www.alfabb.com" or "search terms site:www.alfabb.com//bb/forums/whatever-forum-you-like" and get much better results than AlfaBB could ever provide. A further benefit for the BB is that such resource-intensive and 'computationally expensive' searches are off-loaded from the AlfaBB server and happen at Google's expense.