By Daniel Kline The cruise line has spent big to offer something its rivals simply can’t equal. For some cruise line passengers, the ship is the destination. That’s especially true with Royal Caribbean (RCL) – Get Royal Caribbean Group Report and Carnival Cruise Lines (CCL) – Get Carnival Corporation Report which have steadily raised the bar when it comes to onboard experiences. Carnival has added a roller coaster on its latest, the Mardi Gras, while Royal Caribbean has bumper cars as part of its unique “Seaplex” on Odyssey of the Seas, and an array of new and reimagined experiences on Wonder …