While I posted upthread that a 3 or 4 day cruise will always feel too short, I would disregard the comments that it's not worth it. Short cruises can be a fantastic deal for a quick getaway. It's no different than a 3 or 4 day hotel getaway, IMHO. Sure you'll wish you had more time, but that doesn't mean you shouldn't take the trip at all.

We do 3 and 4 day cruises at least once a year, but to be fair it helps that we don't have to fly to get to the ship.

I would advise you not to limit yourself to only the Disney cruises. Carnival has a wide selection of 3 and 4 day cruises and Royal Caribbean and Norwegian each have one ship doing 3 and 4 day trips.