We went last year during a busy spring break week (Unofficial Guide had Disney parks rated at 8-10 for crowd levels all week). We slept in, got on the road at 11, and got to Kennedy Space center about 12:10. I didn't think crowds were bad at all. We got in line for the bus tour with stop offs that is included with admission (really an excellent tour) // very educational and enjoyable. The line was maybe 20 minutes long (I didn't think that was bad at all). We didn't have that much extra time as we enjoyed the tour a lot and spent quite a bit of time at each of the stops. When we got back, some in our party went on the similator ride and others just checked out the rocket garden and gift shop. Many might want to see more, but this mini half day trip for us was perfect. We were ready to head back and skipped the astronat hall of fame which is open late, and we could have visited.
Boy have they improved this place. 10 year ago based on my experience I would say skip it. I would though now if you have even a slight interest in seeing this facility definately recommend going.
Here's a description of the basic tour. This in itself makes for a great visit:
Short of becoming an astronaut, theres no better way to get a glimpse of Kennedy Space Center than on the Kennedy Space Center Tour (KSC Tour). Take a NASA bus for a panoramic view of space shuttle launch pads at the LC-39 Observation Gantry, and then experience the historic Apollo 8 launch and marvel at a massive 363-foot-long Saturn V moon rocket at the Apollo/Saturn V Center.
The KSC Tour is included with admission and departs every 15 minutes from the Visitor Complex. The tour is self-guided, allowing guests to get off the bus and spend as much time as desired at each location.
Price: Included with Admission