Well I am not sure what the answer is for long term viability of these marque specific clubs. For those of us not in retirement, all we can do is hang on and enjoy the ride. (I am 48)
Let's face it, our hobby is still fairly "young" and is unique. Most car clubs were organized by a few passionate folks years ago with a specific interest. It amazes me that these clubs from the Buick Club, KFOCI, WP Chrysler, Cadillac LaSalle Club and of course AACA among many others - grew so much without the aid of technology.
Now we have technology and the numbers are shrinking. One thing is consistent to me, is that older members tended to gather and enjoy and now many meets are smaller and less attended.
I always wanted to join car clubs so I could get together. You can't own every car. So to me, getting together allows one to experience other cars in the make-specific club.
I don't know, some of these old timey members that are no longer with us, and some of their parts stashes are gone or unaccounted for. I know one thing though that is relevant in my general time frame that has negatively effected the hobby and that's greed or "what is my car worth". It's normal, but regrettable.
That is why I am all for the market for cars staying low. One of my other cars has an avid following where some members want the cars crushed/parted or removed from the marketplace in order to raise the value of the cars they own!
I do not involve myself in order to make money. I want to drive and enjoy the cars. Not saying some of these old time members were greedy, probably not. In their cases - probably the next generation was not interested in the Kaiser products and the chain ended.
THAT, more then anything is the issue. (In my opinion) Most hobbies are personal, within a family. My mom collects "Fire King" cookware. I won't, although I may keep one or two of her pieces around. My dad collects nothing, but takes historical sites trips. So for all cars that are not museum quality cars - with price tags to match - I think you will continue to see a decline in membership to the very rabid among us and - this is among my hot button topics - few if any cars being restored.
Those cars not being restored are making their way to crushers or will in the next 10 years. We have a few old time members with glorified parts cars that once they pass away, the estates will probably quietly send them to the crusher. These cars were probably picked up fairly cheaply if at any cost and if you are an aging member, should be sold or given away to younger members. (Again, my opinion, that's not a demand) In some cases, you see the next generation place unrealistic price tags on the cars and even if you are a longtime KF member and friend, it doesn't matter.
The other problem is - even if these cars are given away, transport has become a huge cost variant. A while back, a nice elderly KF guy from California offered a 51 Golden Dragon project at virtually no cost. I think he wanted $250 for it or so. BUT the cost to transport it to Iowa was in the $1400 range. So, for project KF cars, my pool is limited to maybe 500-700 mile maximum radius. And this is often mentioned in response posts here - the "man, if that car was closer" mantra.
So these are difficult times where those of us with passion for the cars need to do exactly what JoeFrazer says and get them out and drive them AND respond to chapter and regional opportunities to get together.