I don't have a resin printer, but so far my understanding is that the level of details and smoothness of the prints is much better than in the filament prints.
About the 3D models, it's enough to draw it once. Another source of models can be made by scanning the real thing with a laser scanner, in a rail station or in a museum. There is yet another way to reconstruct a 3D model by using many pictures taken from different angles. Then, there might be technical drawings in archives. None of these is perfect, but I guess will require less work than making a model from scratch.
In time, more and more CAD models for trains will accumulate. After all, it doesn't has to be collector's items or copyrighted models, can be fantasy wagons and locomotives that never existed before.
All is needed is to be enough enthusiasts, and to bring them together in a forum or some similar online place. There, they can talk to each other, share pics and videos with miniature landscapes and trains, exchange between them info, models and hardware, etc.