I think a nice thing for Platinum guests on a 7 day cruise would be to choose at least one thing from this list (if you're on a 14 day cruise, choose 2 from list, 21 day cruise, choose 3 from list, etc.)

Just a few ideas (I can come up with lots more :D )
complimentary pre or post cruise hotel stays
complimentary upgrade to BIZ/1st class
complimentary luggage transfer from home to ship and back again
complimentary excursions while on the cruise

These are the type things that are done for full WCers that make it really nice!
Or how about a free 7 or 14 night cruise? or make any 7 or 14 day cruise booked, regardless of itinerary or time of year an automatic 2 for 1.

These are the type things that appeal to me. What are your thoughts??