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All the foolishness and hypothetical examples aside, it's a decision I think one can make only when they own the bike in question. Chuck's previous posts seem logical to me.
Personally, I'd choose to ride any authentic race bike, without much hesitation, regardless of rarity. Those bikes are not built with hardly anything but competition in mind, and I'd feel great out doing some training miles on one. Most true racing bikes look better in a used, if not abused condition. But then, my keen area of interest is in "team issue" type bikes...
Perfectly crafted "show" bikes are in another place in my opinion, all spit and polish, shine and fussiness... don't really care for these kind of bikes, and maybe it's best to leave the parts in their boxes with the wax paper, and not even build them up, lest something get scratched with a spanner? ;-)
All that said, I've always got a "current" spec ride that gets 80 percent of my miles each year, but that's another story!
Grant McLean
Toronto, gov't senators say pot should be legal, Canada