In 17-20 years sandcast 750s will be 60 or 65 K, and Vincent twins will be over 100 K.
I used to do a lot of research into vintage bikes, and had a bit of a grasp of the market and what makes it tick.
I have unearthed a few 5 star bikes, researched them and hunted parts for them.
One I had was made over a 6yr period and there is probably less than 100 on the planet (including project bikes), it went to a very good home, it is now 105 years old.
I have gotten to see some very remarkable bikes in real life.
I dont think I am being an arse on here, just anwering to a subject that you brought up...