I've been following this Venice issue for some time and the above hits a big point. Day trip visitors, whether they arrive by bus, train or cruise ship are not very profitable. They don't rent rooms, they might buy one meal - an inexpensive lunch, and they don't hang around long enough to buy expensive souvenirs. They get that cheap junk made in XXXXXX that we were all criticizing in another thread.
A person who stays overnight (I would recommend two nights minimum) rents a room, buys several dinners, and may have the time to shop for that special souvenir (more $$$'s, but not necessarily so). He/she also gets to see Venice at night, which is magical to say the least.
Venice, like the popular National Parks (Yellowstone for example), follow the same simple rule regarding crowds. The crowds go down with the square of the distance as you get farther away from the Super Star, Must See, Highly Publicized areas.
One warning, if you sit down at a table Piazza San Marco to hear one of the bands that is performing, be prepared to spend 20 euro for an espresso. My child found that out the hard way.
But, it was a great time with new friends.