Are the dichroic films suitable for wet environments, like a shower enclosure? How scratch-resistant are they?

They are fine for wet and damp locations like a shower or the exterior. They do come with a scratch resistant coating which will help, but it does not make them fully indestructible. I would use caution if you will need to clean them all the time. Using a window squeegee when they are wet would be a great, safe way to keep them clean.