Though you have to reserve in advance, Royal Pacific has a free bus to and from Sea World. Otherwise, I'd say Uber for that. But for the Disney, yes, I'd rent a car, pay for the one night parking at Royal Pacific, then return it to the airport. If you use Uber to Disney, I would think the price would not be that bad, it's the end of the night where you would get surge pricing, and traffic will be not so fun. I'd rather come and go in my own rental, then rely on uber, to get to and from the Magic Kingdom.
I rent a car from and back to the airport the whole time. While we don't also do a day or night at Disney, we do like to eat at other then Universal parks, and visit Disney Springs one day. Plus, we want to do the Eye, and other lesser than parks around Universal.
What ever you do, I hope you enjoy your stay at the Royal Pacific. We really like that hotel, and the convenience it is to City Walk and the Universal Parks.
Oh, and by the way, SW is closer to Universal than Disney. Give yourself at least 45 minutes to get to the parking lot for the Magic Kingdom. SW is about 20 minutes or so, depending on traffic. You could take the free bus to SW, and Uber back, if you didn't like the return times.