I believe the OP is onto something. The Baby boomer generation is largely responsible for the popularity of the Collector Car hobby, and many other nostalgic collector item hobbies.
Most of the baby boomer generation is either retired or nearing retirement age. As with most people, when you reach that age, you have a tendency to simplify your life. Selling off car collections is one of those "simplifications".
Beyond that, most younger car "collectors" today, do not amass such large collection of restored cars. I'm not talking about the guy up the street that has 15 cars sitting around on his property. These people are Classic Car Collectors,as much as they are junk collectors. I'm talking about guys like Leno. Guys who not only collect classics and memorable cars, and cars that had some meaning to them as a teen or young adult, but guys who also actively and regularly spend the time and money to restore, hotrod, and maintain ALL of the classic vehicles he owns.
The younger generation doesn't seem to have the same fascinations, desires, and wants that the Baby Boomers have for these cars. Yes, there is a hand full of guys in the younger generations who still appreciate them, but for most kids coming up today, it's the Hondas, Toyotas, Nissans, and other cars that were "THE" desirable cars of their youth that is their passion.
While there are some of the under 30 crowd who still appreciate the Classics and classic muscle cars, MOST of these young guys look to "tuners" for their personal choices. It is what they wanted as teens, and it is what is available for cheap. There is an huge after market contingent of products available, for these cars, used parts are plentiful and still pretty cheap, and decent low millage examples of used cars are also plentiful.
These are guys who were raised with FWD, FI 4 cylinder cars, and transverse mounted V6's. TO them, a V8 is not only unnecessary, but inefficient, heavy, and expensive to operate. Forget about carburetors, they don't have a clue how to work on them, or tune them, and they don't care. These kids are 100% fuel injected.
The Collector car hobby in is flux right now. Many private collections are going to museums instead of private hands, younger people are more interested in the cars of THEIR youth, rather than the cars of our youth, MPG's are replacing torque ratings, and HP ratings of a turbo 4 cylinder can easily mater that of a new Hemi. Hell! Look at Fords Turbo "Ecoboost V6". Presently it make more HP than their 5.4L V8 of only 5 years ago.
While the collector car hobby will continue, what is being collected will slowly change to that which is desirable to the young guys. TODAY'S GENERATIONS of gear heads.
That not to start a role call here of young guys who enjoy the classics, I know there are many, but they, and we, will soon no longer be a majority in the collector car hobby, or numbers are, indeed, dwindling, and being replaced by the under 30 majority of 80's and 90's cars collectors, tuners, and enthusiasts.
Just like we replaced the Pre-WWII enthusiasts, so shall we be replaced. Is it going to happen? Yes. It's only a matter of time.
There is one more ingredient that I have not mentioned, yet, the Federal and state governments. For the last 30 years there has been grumbles form the Environmentalists for laws to limit the age of cars registered and insurable for use on public highways. The range of that age is between 20 year old cars and trucks, to 30 year old cars and trucks. Today, that lobby has been squelched by many of the SEMA members. It's pretty evident that sooner or later some type of legislation is going to be passed to limit the age of cars that can be driven on the public roads. It's going to happen. Maybe not in the next 5 years, but almost certainly in the next 20 years.
We've seen one (very passive) iteration of the Government's involvement in attempting to do away with classics. Obama's "Cash for Clunkers" program took many viable cars off the roads, and, at the same time, reduced used cars and parts availability, that resulted in an increase in the retail prices of both.
When the government mandates an age limit on street legal cars the Collector car hobby will change drastically. These cars will become museum pieces, show vehicles, and parade cars, and will be illegal for use on public roads. There will, of course, be the rebel owner who says "I'm going to drive my car no matter what the law is", and that person will, most likely, lose that car, and his drivers license, if caught.
The 20 (or 30) year rule has been toyed with about dozen times so far, and thanks to the folks at SEMA And other car enthusiast organizations, hit hasn't gotten traction. Let's hope it stays that way, and the government doesn't get into the business of telling us what we can't drive.