Curt,
I am doubtful of those letters stating that F. Masi built a bike. Usually, makers don't write letters like that, as they try to create the impression all their bikes are created equal. That it makes me think it is a forgery. I know of one case where such a letter was forged, for a Masi track bike. (Contact me off list if you'd like details, but I think the case may have been discussed on the list.)
So I would't put any value on such a letter - on the contrary, I would very carefully examine whether the bike is real. Otherwise, I'd prefer craftsmanship over provenance. Exception is a famous rider - if the bike won the Giro d'Italia or something...
Jan