On the other hand, you can argue that what's left preserved is what was left to preserve - by the 1990s, very little NWNGR or Croesor Tramway stuff was left, and the FR Co generally have taken preservation of the remaining heritage structures seriously.
I've noticed that the "big business" end of preservation does seem to try to take its heritage responsibilities more seriously in a museums sense - by which, I mean, try to take their heritage preservation responsibilities in the same way that a professional museum or archaeological service would do. So, you have structures like the Tryfan Jn station building being maintained in their ruined condition, the railway trying to prevent further decay but at the same time not restoring the structure, because current thinking in archaeology is to stabilise sites for the future, without unnecessary destruction-of-evidence either from the elements or from over-zealous restoration. I have to admit that I'm guessing as to the railway's motivation there, but you never know, I might be right!
(the archaeology of railways isn't exactly well-developed compared to other industrial archaeology - the standout-significant event in the subject is still the Liverpool dig from 1980 or so)