Does the Cruise Line Duffy cost more? If not, I'd buy him. But I'm not sure I'd pay more for that shirt....and you're also a captive audience on the cruise ship (if there are no cute Duffys then you won't be able to get one at all until you're back home!).
Then again, getting him on the cruise might make him feel more special than just picking him up from your local store.
So argh! I don't know! I'd personally wait for the cruise, I guess.
(I do personally think the shirt is cute, even though it's not special. If nothing else, you might be able to sell the shirt itself for a nominal fee, if that interests you. Not to me, since I don't have a 17" Duffy, but surely someone somewhere would want it, especially if they're paying $75 for the Cruise Line Duffy!)