I know you will enjoy the Breeze more than MSC. Even if it is just for the cabin size. The pre-cruise hotel in Barcelona is a nice addition. Barcelona is a great city to wander. The Tourist Bus is a great way to get around. We plan on spending more time in the Gothic District on this trip.
Do watch your purse and wallet in Barcelona because there is a bit of a problem with pickpockets. The only time I was "almost" a victim was with a group of children running around. They ran around like they were playing tag and then started bumping into us and one tried to go for my pocket. Once we were on to them they ran away. You don't have to go around in fear but a money belt or neck wallet, under your clothing, is the best way to walk around. Violent crime or muggings are VERY uncommon. Regardless, Barcelona is a beautiful city to enjoy.