You and I and most here see things from a preservationist's perspective. That might be entirely different from the "average joe" who is house shopping and so the profitability of these decisions often favors products that are new and in stock and that contractors are familiar with.
Some of the things we take on are such big projects that you just have to do the best you can and to try to make balanced decisions and each of us has a different set of factors. How much we preserve is important, but in some cases good financial decisions fly in the face of restoration VS new.
Im doing my roof for example. Id so much rather do shakes than new asphalt shingles. I'd like to rip out the metal gutters and put wood ones. Finances don't support that so more asphalt shingles and tin gutters it is... If I win the lottery I'll have that wood roof because I'd much prefer it. In picking the flashings. Plastic ones are cheaper, but Ill go for metal even if the plastic will last, it would feel like an old house sin.
Every time we turn around we face little decisions like this.
Copper or pex? painted rim or months of scraping. There is no end so part of it has to make you happy. One thing we can often afford to invest is a bit more of our own time to make it right. I don't think I'd go to the extent of re-wiring with knob and tube, although it could be done safely. Plaster or drywall? The right decisions depends on more than which is more original and for some it could easily vary depending on the conditions.
Phil