I would expand the itineraries and start or increase cruises to/from South America, Asia and Australia.
Carnival has a good product that people enjoy but it is very "Caribbean centric".
I don't know how good a business decision this would be for Carnival but it would be something "I'm" interested in.
BTW: Carnival has lost a lot of its party image. Seven day, or longer cruises, when kids and younger folks are not in school have a somewhat older and not so party hardy types of people.
I have been on a Carnival Pride cruise that I would guess had an older demographic than Celebrity cruises I've been on.