I would agree with Dave. If you book a normal cabin and go the first day you can buy day passes. Note that the gym, saunas in the locker room are still free, so the only thing it buys you would be the extra steam rooms, the hot beds, the thermaslasaooosphy ?? .. dang it - the big jacuzzi pool.
If you are going to partake in those then it can be worth it. The other benefit is the balconies are non smoking so you don't get smoked out by an up wind neighbor.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013