In eager anticipation of your next cruise, you've logged into Norwegian Cruise Line's online cruise planner, and you're greeted by words in big bold letters:  "LET'S GET YOU UPGRADED!" Those first four words grab your attention with a promise of a better cabin than the one you've already booked. Then your eyes move on to the words "Submit an Offer ... " and you realize that you'll have to shell out some money for that upgrade. The big question is, should you submit an offer to upgrade your