As mentioned, once someone reaches their mid-40's (men for the most part), they start yearning for their 'toys' from earlier days. It's a rolling range. I see this with old cars too. I noticed now that the late 1970's Pontiac Trans-Ams are fetching more money than my 1971 Plymouth RoadRunner. You can buy a fully-restored functional Ford Model A for $10,000. Not a lot of people left who remember these from their younger days!
Another interesting idea someone mentioned somewhere: The current sports cars should become the collector cars in the future. A problem is that nobody will be reproducing the computerized components found in today's cars (and cars from the mid-1980's onward). This may not sound big, but a lot of guys are into collecting cars as originally delivered.
You will always have a smaller crowd that still appreciates (appreciates enough to purchase) items that pre-date their childhood. I really like Standard Gauge, but compared to other scales, definitely a niche market.