There is definitely something to be said for visiting a city more than once. It is often the case that you will go on a city break and then tick that destination off your list of places to go when you get home. However, city breaks are not just about seeing the sights. They are also about experiencing the flavour of the city.
This is something that you can only do in part on your first visit. After all, the flavour of the city could be entirely different in a different season when other exciting things are going on and the mood of the city changes.