Can any of us name a single type of motorcycle (or car) made up to 1946 that has fallen in value over the years because the people that bought them and loved them new are gone now?
The exact same is true of the bikes we knew and loved. People are picking up the torch every single day for these things. Prices can vary year by year because of economics and silly fads (XKE roadsters were $30,000 here in 1990, $90,000 by 1995, and $45,000 in 2000) but long term? No way any of them "lose value". Never happened yet.