Certainly, if we compare durability and stability corrosion of the restored detail and the new one advantage as a result will be for the last one. But we've got here a non-typical situation. Firstly, some spare parts cannot be bought for the reason that they are no longer produced, and secondly some parts are simply elements of the body and couldn't be replaced at all.
Details
As for the metal work, it is important to make the geometry of the new part close to the geometry of the original. That is to avoid subsequently use of thick layers if putty which should carry out only function of finishing alignment, instead of replacements of pieces of metal.
At present all is more or less corrected, including the damaged rear fender. It has been extended in several stages, not giving metal get “tired”.