Lovely Bicycle! - a great blog bicycles and cycling, just had an interesting post about the restoring of older bicycles. They broke it down to 4 main categories-
The Full Restoration Approach-Make as original as it was when first built, replace worn parts with exact replacements of what it originally came it.
The All-Original Approach- Keep it all original, as the title suggest. Replace nothing, even if it means the bike then become obsolete.
The Period-Appropriate Approach-A restoration that is looser, does not have to be exact, but outfitted with parts that would be of the same time period as the frame.
The Updated Remix Approach- This is an anything goes approach. Bike is personalized and set up to suit the rider, no restrictions on what the bike was originally.
Read the original article-Refurbishing Vintage Bicycles: Different Perspectives
I love an all original bicycle, unrestored, of course. Most of my bikes fall into that category, but I do have to update perishables such as tires and brakepads, to make them ride able. I do have one bike, my chrome Rochet, that is anything but original. It was originally an early 1960s 10 speed bicycle and I have since turned it into a commuter, with upright handlebars, alloy fenders, fixed gear wheels, and porteur chaincase. It is a far cry from what it was originally.