Every bike that I have sold(Tempo, Super Sport, PFN10, Gitane Super Corsa, Davidson Impulse, Alpina 5.5, etc.)has been bought by a young man in his twenties. I think their will continue to be a good market for vintage steel with a slow gradual rise in prices for rider grade bikes.
Collector grade bikes may tend to reach a plateau. When they go over $1,000 they compete with a lot of other toys. They may keep pace with inflation.
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1973 Schwinn Super Sport
1986 Schwinn Peloton
1976 Raleigh Super Course Mk II(for wife)
1983 Gitane Super Corsa
1991 Trek 750 Multitrack