Daniel-
Reference Bob Hovey's Masi site pages for some good info.
http://bhovey.com/
Beyond that, the Prestige morphed over time, but were indeed essentially a non USA market item save for a small number. They were it seemed imported into Canada. The top tubes got larger in diameter at some point, I don't know when.
The Volumetricas were Italian built, at the onset, there were some made in the USA, and some in Italy for USA Masi but by others than the Masi Vigorelli.
As to collectable value?
Probably an early Italian Volumetrica on top, with Excel tubing even more. Next, an early Prestige, but these bikes seem to not get the attention they deserve for whatever reason.
After that?
What you like, and what fits.
John Jorgensen
Torrance CA USA