There is a lot effort going into documenting the cars and factory processes and so.
Also a lot effort in factory registers (e.g. think Marti).
But what about digging up the original tooling and save it? Is it gone? Scrapped? Everything? Is some of it languishing in an obscure warehouse somewhere? The best reproduction parts will be made from original tooling. If research also went into the exact materials used, it would be genuine RE-production. AFAIK not many efforts go into this detective field of the hobby.
Reproduction parts need to be made by enthusiasts not business people. I believe ROI always will be lean if not negative for real quality reproduction, at least if tooling is involved.