I don't have Platinum or Gold, but I do have 4 other Amex cards, I recently got a Cunard, Royal Caribbean, and Regent offer.
Best advice I can give on any of these offers, being for cruise or anything else, if you see something you think you might remotely use, add it to your card. You never know how long the offer will be there, although the expiration date for the offer may be a couple of months.