Gut the entire space start from scratch, this option can range anywhere from $10,000- $20,000 or beyond depending on your choices. If you go with this option be careful, because although you might love toile wallpaper and aqua blue subway tile, the new owner could come in and take a sledge hammer to it before the grout has time to cure. So if your investing in a total bathroom remodel think resale. Your choices for flooring, fixtures, tile, vanities, etc should be neutral and appeal to the masses. You can still bring in your personality with the accessories, area rugs, towels, etc.
If you do not want to make a $20,000 investment into your future,there is still hope for your poor bathroom. RE-DECORATE. The first thing would be to put a fresh coat of paint. I LOVE PAINT, its magical. Paint can camouflage, accentuate, and tranform any space affordably. Sherwin Williams has some nice shades to compliment bathrooms: MODERN GRAY SW 7632, MINERAL DEPOSIT SW7652, LEMONGRASS SW7732, CHINADOLL SW7517