With unjustified apologies to the fixed/ss culture, I'd agree with most posters; it doesn't make a whole lot of sense to go through the effort and expense upgrading an old bike, especially when it comes to drivetrain upgrades, due to the many compatibility pitfalls involved. As a side note, paying a professional to do it for you would be like paying a shop to drop a z06 engine/ZF 6-speed/irs in a '68 Nova. Not many will understand why you bothered, and didn't just buy a new vette and enjoy it along with all the other advancements.
That being said, it's your bike, not some sacred icon of antiquity; go ahead and do what you want with it, if it helps you enjoy your ride. Hang on to old parts if for no other reason than to attract a nostalgic buyer, or put them back on just for the fun of it(?), some forlorn, rainy day to reminisce about youthful, vigorous days long passed.
Upper-end vintage (ususally racing) bikes definitely lose value in the eyes of top-dollar-spending nostalgic buyers if any original components are lost/missing/damaged/bent/worn.
Some of the UJBB's (ubiquitous japanes boom bikes), though, can be so obscure, no one will really care what anybody did to it, unless it was an unassembled, in-box NOS, and then still limited to a small audience whose numbers eventually decrease as time inexorably proceeds.