+1 to what Le chuck said--as a home inspector I see what people like and don't like everyday--stealing a bedroom for a second bathroom is a bit of a wash and you wouldn't get your money out--a second bathroom somehow is the way to go. Also,double check your code--almost all old houses had stacked bathrooms and the vent became a "wet vent" meaning that periodically the upstairs used the venting portion of the downstairs vent stack. Otherwise, you would have had 2 x 4" cast iron vents in the wall side by side. Maybe on "new" construction its no longer allowed, but compare that to a cheater vent or a new vent installation and I'll take a wet vent anyday..