First I would get Jim Berra off his "behind" and get a decent Milestone Rewards program in place.
You have to give folks something they WANT to work towards and something that is worth the continued loyalty.
Secondly, I would teach some CONSISTANCY in the areas of Debarkation and Repeater's Parties. Carnival is missing a golden opportunity at their Repeater's Parties to push the product and it not cost them a thing. Some CD's handle it very well...others do as little as possible.
AND, if I were Mickey Arison, I would implement reciprocating perks to sister cruise lines. (each cruise line would have their own set number that this would happen at)
Princess and Cunard already have this.....
Even if it were 50 cruises for Carnival folks to achieve this, it would be an incentive to go "up the food chain" to the more expensive sister cruise lines.
At the same time, it would give Carnival folks something else to work towards AND since anyone who has done 50 cruises on Carnival clearly love the product....the Carnival cruiser would still continue to sail with Carnival as well.