We did land and sea last February, 4 days at sea and loved it. Hated the 6 am immigration thing on the last day, especially with small kids but they napped on our way back to Orlando. We had thought about doing a day at the beach but had such a nice,full day at CC that decided to do DTD instead since we hadn't had time during our land portion. And we honestly felt better about that since we were so much closer to the airport and didn't have to worry about traffic, etc.
You could also go to Canaveral base for a tour, but it was about $100 US for the 4 of us and we decided to spend the $$ on souveniers at DTD instead.
Enjoy the cruise, it is truly magical. If you are doing land and sea option then you pre-board from AK, but it sounds like you are just doing them separately. We boarded at 3:30 pm and it was too late to really enjoy the day on the boat and the sail away party, since I had to unpack our clothes for early seating dinner. So my advice is to get the clothes unpacked as soon as the bags get to your room and enjoy that sail away party!