We spent 2 days at Kennedy Space Center before cruising on our 7 day Star Wars cruise in February 2019. It was amazing and we had SUCH a great time. We were fresh, so walking all day wasn't an issue (and the cruise thereafter was a nice relaxation). Note that for us (2 adults), it was CHEAPER to buy the annual pass than to purchase 2 single day tickets. Also, if you have the time, check the visitor's center at Kennedy Space Center - we were able to snag tickets to see a SpaceX rocket launch that night (note...do NOT use binoculars for a night launch...I saw spots for about 1/2 hour!! LOL).
We also rented a car, which was really helpful. Not sure how easy it is to get an Uber/Lyft or other transportation.
If you've never been and you're a space nerd like us, it's a GREAT addition to your trip!