Simply put, original is better when considering collectable value. However, there are situations where this is not feasible. I have a '75 Moulton (his 16th production frame, and his first "touring" bike). When I got it, the fork blades had started to separate from the crown, and the paint was heavily oxidized. If the fork had not needed re-brazing, I would have left it. Luckily, it was also rather thick, not like alot of the thin production sprays of the time. CyclArt did a good job of matching the original color (from the fork tube), and the paint thickness is close to original. The I am hoping the gloss (which is not consideder "high-gloss" by todays standards, fades soon.
Before:





After:





I have it about 60% re-assembled, but need to replace the old steel Weinmann fenders. I have not had any luck finding any, and may have to give up and use Velo Orange or Tanaka.