You mentioned that it would cost you an "extra $1000" to do the cruise although that's not an entirely acurate way to look at it. For the cruise portion of your vacation your meals are covered. If you do land only, you will have to budget a certain amount to eat.
If you take the cruise, you may be more likely to want to do excursions in Nassau that would be an additional expense that you wouldn't have land only . . . of course souvies do add up at Disney World too.
Is this a "once in a lifetime" type of vacation? If so, you are somewhat short-changing both experiences by only having 3-4 days each.
What ages are the rest of your family?
I have to echo that
Disneyland is similar to the Magic Kingdom at WDW. If your family enjoyed that experience they will want 1-2 days to see the Magic Kingdom.
Animal Kingdom can be done in a half day if you just want to hit the major attractions. But if you're a stop and smell the roses kind of person, nothing less than a day will do.
Staying at the Beach Club puts you right in EPCOT's backyard where some of the most amazing dining awaits you. I couldn't spend less than 2 days here as there is so much to soak in.
You might enjoy an afternoon of just the pool area at the Beach Club, it's a destination to itself.
Then there's MGM with one of the best nighttime shows ever.
I love cruising and can't wait to get back on the ship, but I would definitely want to be able to experience WDW the first time with at least a week (I'll be visiting for my 12 visit this fall for 2 weeks).
Is the rest of your family anxious to experience cruising? Have you done it on another line before? Maybe it's best to put WDW on the back burner for another time and just enjoy the 7 day cruise.
My vote? Devote the week to one vacation or the other, don't try to combine the two when you've never done either one.
Unless of course, you have the option to repeat one the other or both within two years . . .then it's just a great "taster" of a vacation for you.