People have restored much worse-looking bathrooms to original, and have made them completely new-looking. Here are some threads that might help you out:
And in cases where things were too far gone to save, others have pulled it all out, and replaced with more contemporary furnishings.
One thing that is helpful, is that if you do end up pulling it all out in order to start over, be as careful as you can, and then offer those parts up either for sale or for free, so that other Airstreamers who are trying to restore their coaches to original condition, might have a chance to acquire the parts. As I'm sure you can tell, it is quite custom, and many of the parts are now difficult or impossible to obtain.
Good luck with whatever you decide!