...something that is likely to be debated ad nauseam until the end of time. Like anything else 'vintage', it will ultimately depend on what the buyer is looking for. This same kind of debate rages on and on in an antique radio forum that I belong to: whether it's more valuable if it's left 'all original', even though it doesn't work, or if it's not 100% original (has new parts installed, not normally visible), but working...some folks even go as far as 'restuffing' components, that is, hiding new components inside the shells of the old ones, to preserve the 'all-original' appearance (however, that would be significantly more difficult to do with a bike than with a radio!)...
...some folks are that anal about 'all original' and think that preserving its originality is more important than restoring it to working order...and especially more important to making significant changes to it, even though they actually make it work better...whether you're dealing with vintage radios, vintage bikes, or vintage...whatever..., you might occasionally encounter that kind of 'anal' buyer, but I think the majority of folks want it to be working, and working well...
...I personally fall into the 'working well is more important than 100% original' camp...unless, as previously stated, it is something that is EXTREMELY rare...