Thanks everyone for all of your input. I thought I'd update with some of the ideas that I've compiled based on reviews here and other reviews(trip advisor, prior disboard posts, etc.) Please comment or add other suggestions/reviews.
Here are some possibilities we're considering:
San Juan: fly in 2-4 days early. Rent a car. Take Bio Bay tour, Taste of San Juan food tour, possibly El Yunque rainforest, and El Morro. (We're going on our first Eastern Caribbean trip in 1/2015, so we have plans to see both forts on our San Juan day.)
Barbados:
Calabazza Sailing/Snorkeling (or Silver Moon Charters)
Grenada:
hike/swim Seven Sister Falls
possibly hire a recommended tour guide: Mandoo's Tours, Sunsation Tours, or AJ Meddy
Martinique:
this is a tough one, since most websites and trip advisor reviews are in French.
possibly rent a car and snorkel a black sand beach(Anse Couleuvre)
or
visit a floral gardens Jardin de Balata (possibly take public bus that runs there)
Antigua:
Valley Church Beach - free, chairs $5, umbrella $15, cab $50 r/t
or
Antigua Paddles - Boat, Hike, Snorkel, Beach, Boat, Kayak (
DCL excursion)
St. Kitts:
Royston Tours: 4 hr. tour w/lunch & drinks $45/pp
or
Day Pass to Marriott: $35/adult(kids free) or $125/family with room
$30 cab r/t
Of course this is just preliminary, since we're over a year away...but it was great fun to start the daydreaming!
Jennifer