Interestingly, the only park we didn't do twice when there over Easter was Animal Kingdom, but that's the one I can actually think of the most reasons to visit twice. The animals are never the same each time, and with the nighttime entertainment and extended hours coming, I think I could easily visit AK twice. But I love animals, so I'm fond of the park for that reason alone. I don't really ride the rides, except the Safari. If I had time, I'd also include going over to AKL for a visit and maybe a meal.
I only really care about the World Showcase in Epcot, and Hollywood Studios nighttime shows, so those two likely wouldn't get more than one day.
I could go to Magic Kingdom every day of my life. LOL.