On thing that I like in a vintage bike is the use of braze-on fittings instead of using clamps; i.e. clamp-on bottle cages or cable guides or shift levers. As a general rule, the clamp-on devices are an opportunity to nick the paint or accumulate crud and moisture, both of which cause paint damage and promote corrosion. This is more of a concern for bikes that get ridden in all conditions, versus the "sunny day only" status of most of my vintage bikes. This might be a result of my experience with my trusty Raleigh Gran Sport that I enjoyed for 14 years.
Another effect of clamp-on fittings: pump pegs, and the tendency to tear up Reynolds tubing decals at the top of the seat tube. It's not just me, is it?? Frame-fit pumps were definitely an improvement.
I will say that the use of braze-on fittings seemed to wax and wane over the years. The braze-on fittings for the rear brake cables on my Raleighs existed at the same time that top tube cable clamps were popular.
here's a shot of the braze-on stops for the rear brake cable on my '74 Raleigh International, as well as the T.A. handlebar bottle cage that I use to avoid clamping a bottle cage on this bike's down tube. I really like this h'bar bottle cage!
Steve in Peoria