When I started playing deity level I finally found a valid reason to build the Hanging Gardens. Since the city does not go into unrest unless the number of unhappy people exceeded the number of happy people, you could have a luxury rate of zero percent with no entertainers and all of your size one and two cities would be fine.
I later found that if you have no unhappy people in a city then the president's day celebrations could grow that city's size fairly well.
I later found that if you have no unhappy people in a city then the president's day celebrations could grow that city's size fairly well.