The ships almost always sail full, or pretty close to full. So your chances of getting an upgrade at the pier are slim. If you picked a specific cabin they will not upgrade you without your permission (because they believe you picked that cabin for a reason).
I agree. If you really want a balcony call your TA and ask how much it would cost to upgrade before you get to the pier.
We received the upgrades before we left. Got it with the doc's. We were very pleased. Still inside rooms but on the Empress deck instead of the Riviera. It was wonderful. Also when we returned home, i emailed Carnival to let them know the service was good and the ship was great and we all had a very good time. I just received a large envelope with certificates for free excursions on our next cruise. These are for the group of 10 of us that went in May. Carnival is the best! We are already planning our next cruise and have almost 25 people going this time. Our group is multiplying... Happy cruising.. Char