Hi--we just took a land/sea in October and loved it! But, I actually am thinking of it differently now, so I'll give you some things to think about . . . . .
We did the land first for many of the reasons most people are giving--you run around at the parks, and then you get the relaxing part last. Well, we ran around SO much at the parks, we felt like sleeping through our whole cruise!!! My DD5 fell asleep at dinner every night (we had late seating) and my DS9 was not that far behind. When Sunday came, it seemed very unmonumental to get in our car at 8:00 in the morning and drive home. Now, don't get me wrong, we had a wonderful time and loved both parts of the trip!
The packing was a bit hard as well, b/c the cruise has a lot more things that you have to pack, dressier clothes, etc., and things you can't just run down to the store and buy. So the morning we were leaving for the cruise, it was hard to pull it together to make sure we had everything we needed to take with us (we drove so we could leave some of our luggage.)
So. . . . . on our cruise next May, we are going to WDW AFTER the cruise. I think of it like going to the beach--at first you just want to get there, sit on the beach and do nothing, and then after a couple days, you might be ready to tool around town or do some activities. It gives us something to look forward to at the end of the trip, makes packing easier for me (t-shirts and shorts at WDW), and lets me relax right off the bat and enjoy the vacation.
Just a thought---HTH!
Amy