Many changes were done at a point in time when today's classic or vintage bikes were just used bikes that were not up to date.

They needed paint, got modified.

If still original today, then the quantity of other examples if any would guide a decision.

I had bikes from the 70's that were just used bikes in the mid 80's they got updated to a point. I was hesitant to spread my own from 120 mm to 126 mm but that was just me, having ultra 6 freewheels made the decision to keep the original spacing was easy.

I have sent frames back to the factory in the day and add ons were no problem for the builder.

If you want to maintain a bike for maximum value in the near future, then leave it alone.

Personally I am entertaining the idea of keeping an old rare classic more useful by going to modern cranks and aero brake levers, the latest from Cane Creek and others can even be had with "gum" hoods, they are better ergonomically. I can always restore the bike to original later.
I don't NEED index shifting. but I do think there would be a market for a 126 mm O.L.D. rear hub that accepted a reduced modern cassette (less a cog or two) then I could go ergo without going from 120 to 130 mm .... I wonder of the electra hubs could be reworked...