The elsinore's do have an exceptional reputation in the motorcross world history, that I know.
The '69 750's were, indeed, the world's first and coined the definition " superbike" for the masses. To the detriment of triumph and norton....and almost harley......
'69 750 sandcast examples are in the $30,000 range, depending on condition.
A 1975 "K" model, mint Honda 550 went for $9500 on Bring-a-Trailer a few weeks ago
My original, unrestored, mint 1975 "F" model cost me $700 in 1994....
Vintage hondas are moving up in desirability, especially the trails and mini-bikes.......