I've done two Travel Packages to Hawaii - Marriott Kauai and Renaissance Wailea. Both of those trips were wonderful. Marriott Kauai had plenty of activities organized itself, and Renaissance Wailea is walking distance from the old Outrigger (now branded a Marriott), which is where a ton of activities (snorkel cruises, etc.) depart from.
Ren Wailea has been rumored to be renovated and rebranding as a Starwood, but it might still be on the board for Marriott rewards this fall. I don't know... Personally, I did not consider that Outrigger up to par for what I expect out of a Marriott, but I think some folks here have written good reviews of it recently. My experience is simply walking its grounds before it converted to Marriott - no actual stay there.
Award tix from the U.S. could be tough in December through March.
Another good option could be Europe - I love going to Europe in the offseason. March in Paris, London in December - I've done both of those a couple of times. The trade-off for crappy weather is easy access to any activity, show, restaurant, etc. you might be interested in. Plus premium cabin award tix are quite doable. Plus London gets dressed up for Christmas, which is cool, and sometimes March weather in Paris isn't as bad as you'd expect.
In any case, the difference between a Cat 1-5 award and a Cat 7 award is less than 20%, so I'd definitely go for the whole enchilada and stay in a property you ordinarily wouldn't book with you own money.