We just cruised the 7-day on 11/8/03 and did check at the pier about upgrades.
We were booked in 2 category 9's. The only thing they had left were 1 bedroom suites (Cat. 4?). It was going to cost $1500/cabin to upgrade.
We said, "thanks, but no thanks".
I know they had other rooms available because a pipe burst about midnight on Saturday and quite a few rooms on Deck 5 were flooded and those people were moved. At that time, a sign went up at guest services saying Mickey had a full ship and no upgrades were available. However, on Wednesday night, when our tablemate's DH got sick, and was quarantined, she and DD were given an inside room to spend the night. So, a full ship does have some room available for emergencies (thank goodness).