For every collector that passes on, there needs to be an equal number of new collectors or new money to absorb that supply of old trains that come into the train market. If not, then the supply begins to outstrip the demand. If a collector dies with a $100,000 train collection and those trains come onto the market, there needs to be 10 people with $10,000 each to absorb his collection without putting any of their collections into the market. Just browse the auction websites, (not the bay), and see what some of this stuff is going for.
In addition, Lionel, MTH, etc are also making new releases of the old products, which further dilutes the demand for the originals. Consider how many re-makes of the postwar N&W 746 engine have been made.
Also, the newer engines with all the electronics and features that are different from any post or prewar trains, are another drain on the demand for the older originals.
Since 1969 there have been ample substitutes available to satisfy the demand for many of the original postwar and prewar trains. Postwar and prewar that are mint in the box or like new in the box will probably always have a demand from collectors and investors, but probably not like it was in the late 70s to mid 90s, IMHO.
It's best to buy what you enjoy without thoughts of investment, resale, or inheritance. Play with them and take care of them. Teach your kids and grandkids all about them, and how to take care of them.
To me, there is nothing more picturesque, than watching a young person or a child handling a train as if were fine china.
