I was in Rome and Florence over the New Year's holidays. I stayed very close to the Vatican and can attest to the cleanlines of St. Peter's Square. That area also had Vatican police around at all times. Just outside of Vatican City you will find homeless people laying in the front of building entrances. The homeless scene reminded me of parts of San Francisco. As far as tourist littering and leaving crumbs around the squares in Florence, I would suggest that the city create an area for tourists to gather. I found few places where one could sit and eat or even linger for very long. It is no wonder people use the "great treasures" as resting/eating points. The area near the Medici family home is near a large town square, yet one can not find a public resting place other than the church steps. The nearest pay for use, public restroom is several blocks away.
All in all, I think as long as the neighbors still care enough to want to clean up the neighborhood, that things are not out of control. Hopefully, a solution will be found that will be able to benefit both tourists, homeless and other people who live /work in the area.