If you go to the Space Center be sure you take the bus tour. It takes a few hours, but the bus makes many stops and lets you off to explore at each stop. You would miss half the stuff at the Space Center if you don't take the bus tour. Plenty of buses, lots of bus schedules so you can pretty much come and go between bus stops as you want. You don't have to stay on the same bus. You can catch any bus at any stop. They all follow the same routes (one big circle route covering most of the Space Center property). You can see gators in the ditch alongside the roads if you watch closely. You can watch them build and go inside part of the International Space Station on the bus tour. You can also visit a huge exhibit/museum at one of the bus stops.

Also, you might want to take a side trip to the Astronauts Hall of Fame next door to the Space Center. You will see it on your right, before you cross the intracoastal waterway on your way to the Space Center. It was really interesting like a space museum with lots of astronaut memorabilia and moon rocks and stuff to see. They even had a Space Cadet school for kids. My wife took a ride in the astronatus training centrifuge and pulled too many Gs. She was happy to get off when the ride stopped. I wasn't crazy enough to try it. We spent about 4 hours at the Astronaut Museum and it's not very expensive. $10 - $15 for an adult when we went last year.