As a relative newcomer to the club, and as an "outsider" (i.e. I have no history with, no axe to grind and no friendships with etc.) I feel the club has an image problem which may account for part of the problem in getting folk involved. From the outside it appears very much as a group for older folk who already know each other and wish to meet up for a pleasant weekend once a year - the coverage of the National Rally tends to perpetuate this image... I may be wrong but it is how it appears to me personally so no point in arguing the facts and no offence meant.
Having no presence on Facebook or many other modern means of communication will only help reinforce that image.
The current forum is "clunky" in its operation and doesn't invite the casual dipping in and out that something like Facebook is particularly well set up for - especially for younger folk who are used to the medium.
I regularly visit this forum and rarely find anything engaging going on, I may try and answer a tech' question or similar but there is nowt in the way of news or amusing stories - I also regularly visit the Facebook page which in comparison is brighter, more colourful and more active (or at least feels that way).

Having said the above, despite using it regularly I am not a fan of Facebook generally and consider forums to be far better for various things. "Conversation" is easy on Facebook, archiving isn't... a quick query regarding a technical problem or a hastily organised social meet is probably easier on Facebook; a collection of pic's of all the various cars owned by members would be far better suited to the forum. Maybe the forum could be made more interesting with more regular contributions? Maybe more picture threads would entice folk in? However, I believe that the use of forums like this one is on the decline as newer forms of social media have taken over, much like the decline of compact disc in the wake of downloads... I don't know the answers - maybe, much like the club in general, the more effort you put in the more reward you get out... Let's give it a try then...