Stick and peel flooring in a bathroom…. Probably not a good idea, unless there is some very good product out there that I’ve never heard of. Wallpaper - maybe. Do you mean a valence on the window? Probably won’t add much. The most dated thing is that light fixture above the mirror. Can those glass shades be removed and replaced with a simpler cylinder style? I’ve seen inexpensive options - clear or seeded at the big home stores.

If you want to remove the mirror and replace it with framed mirrors, call your local glass company. The have large suction cups which will pull the mirror off. However, you should be prepared to patch the wall behind it and prime and paint. Mirror like that should have been attached to the wall with black mastic which will damage the drywall behind it. If you are going to do this, I would recommend replacing the light fixture with sconces. Yes, it will add to the cost to have an electrician rewire and a glass company remove the mirror. But it sounds like you are unhappy. At least get prices for these changes and then you can decide.

Cheapest fix is paint. Pick a dark and moody color...