In your case, I'd stick with the 14 nt WDW stay--something you know you'll love and is worth the cost to you. I think a 3 nt cruise is too short, where you've just finished unpacking and it's time to pack it up again. Our first 2
DCL cruises were 7 nts: Alaska, and Baltic Sea. We booked for the ports and for the Disney aspect. We loved that we could unpack once, but visit multiple locations. We could justify the cost that way as the cruise is covering our transportation, hotel, meals, and entertainment. DH really didn't think he'd enjoy our first cruise, but knew he'd love the Alaska aspect--we ended up loving all aspects of the cruise.
I do understand that it's hard to justify the cost for a DCL cruise, especially if you have to book 2 rooms. We have a 4 nt Dream cruise booked for this summer, as timing/cost didn't work out to do any of the cruises I'd really like to do and we have an expiring placeholder booking that gives us 10% off. I was able to justify the cost for us because we can extend it with a 'cheap' trip to Disney. We're DVC (Disney timeshare) members, currently have Annual Passes--so doing time at Disney before isn't costing us extra (other than food and souvenirs)--we're doing 5 nts in a studio, 4 nts in a 1 bedroom (for laundry), 4 nts on the cruise, and then 1 nt in a studio (due to flight schedules.) While the ports aren't really a draw for us this time (other than seeing
Castaway Cay.), we get to experience new things--the bigger ship with the mini golf and midship detective agency, new theater shows, a pirate night, and a verandah room for the first time (Magic/Wonder verandah rooms cost thousands of dollars more than the oceanview rooms we got! The Dream verandah room was a cheap enough upgrade for us to do it!)