It's about a 50-60 minute ride. If you have an interest in the Space program or history in general, then you will absolutely love the Kennedy space center. I had grown up during the 60's, so going to Cape Kennedy was always on my list. I brought my daughter with me back in 01, and she was 10 at the time, she enjoyed herself. Although, when I asked if she would go back with me, let's just say at this time, she wasn't to moved by the idea.....maybe in 05.
Plan on staying the day. There is so much to see, that it's impossible to do, all the different tours they have. So, pick one that you would like to do the most and have some fun.
When you see the Saturn 5 Rocket and the Launch Assembly Building, your just blow away by the shear magnitude of their size.
I can't waite to go back! IMO it's well worth the visit.
Enjoy!