As many people involved with vintage bikes know, complete bicycles often are worth less than their parts sold separately. While this is not true of all vintage bikes, it is true of many.
So that leads to a hard question: is there a point at which a bicycle's history is too great to allow its owner to part it out, even if the parts are quite valuable?
I think the answer is, "yes". It is hard to determine at what point a bicycle becomes too historically significant to part out, but there certainly must be a point when that is true.
A case in point: a 100 year old bicycle was recently parted out and sold in pieces on an internet bicycle website. While the bicycle was not 100% that age, much of it was. I certainly do think a mostly complete, 100 year old bicycle, is too significant to part out for money.
But let's make this harder, what about a 50 years old Raleigh-built Phillips? The bike certainly is not all that valuable probably, but then 50 years is a long time for a complete bike. What about a 40 year old 10 speed Peugeot UO-8? Such a bike certainly is nothing special, but then it is old and complete. These are the hard questions because it is not easy to draw a line on semi-recent, common bicycles.
What about ladies' bikes? They generally aren't worth as much, and some have valuable parts. Should they be parted out? Is there a different line drawn for a men's bike than there is for a ladies' bike?
Perhaps we have become too cavalier in parting-out complete bicycles, even mundane, English three speeds.
I don't have all the answers to these questions, but I like think about this once in awhile. I will admit my bias is for keeping bikes together overall. I do change parts and make "period" upgrades, but I keep the original parts on hand to reset the bike to original, whenever I need to do that.
I do recognize that there is a need for a parts market to complete old bike projects, but perhaps we are handling certain pieces of manufacturing history when we handle old bikes. I think we should always be respectful of that fact, at least to some degree.