Having lived in a neighborhood where parking was scarce and parking wars were common, I wonder how much that has to do with the Shabbos house.
6 or 7 extra cars parked on a crowded street from before sunset Friday to Sunday morning are going to create problems. I lived near a National Guard Armory. I stayed home on Guard weekends, because there was no place to park. If the Shabbos house is creating a parking problem, someone is going to have to find solutions. Perhaps guests could park their cars in the hospital lot over the weekend.
I lived near a Ronald McDonald house too. Neighbors complained when the house was built. They were afraid of noise from ambulances. That didn't happen. The Ronald McDonald house, by the way, has a parking lot.