First, I'd need some information: At which WDW park do you plan to spend most of your time? If you say Magic Kingdom, I'd suggest upgrading to Wilderness Lodge. If you say Epcot/MGM, I'd suggest upgrading to the Dolphin, Swan, or Beach Club. These places will be much closer, the rooms will be much bigger and nicer, and you'll have nicer amenities. Additionally, you'll have better dining choices.
The cruise, on the other hand, will give the same meals and amenities to all passengers regardless of their cabin level.
Another poster suggested staying in the cheap-o rooms in BOTH places and using the money for souveniers or fun excursions. There's some logic there! How much do you expect to use your rooms?
I also agree with the person who says she analyzes things using a cost/benefit ratio. Will the added cost give you that much added "wow factor"? Personally, we could afford the Walt Disney Suite on
DCL, but we'll be staying in a Category 6 instead (lowest priced verandah cabin that'll hold four people). Why? It's half the price, and we wouldn't get twice the cruise from a nicer room! Just because we HAVE the money doesn't mean we should spend it.