When we originally planned our Paris/Italy swing, I was told by many people that Venice was skippable. It's a tourist trap, it's hot, it smells, and we wouldn't enjoy it. I scheduled two days there and got a bit nervous after hearing everything. However, I can say we both completely enjoyed the city. Two days was the perfect amount of time, and any more probably would have had us bored with the city.
It felt like we were walking on a Hollywood movie set. Alleyways that couldn't be streets were just that. Small bridges connecting to other small bridges leading to a row of restaurants and cafes that looked like they didn't belong.