I've been. Security is VERY tight now, stricter than I've seen at most airports. No backpacks or coolers allowed. No lockers provided anymore. But once inside, I didn't notice any difference in terms of security.
The main tour has been shortened, with the international space station dropped. That part is probably gone for good. As of a few weeks ago, the two specialty tours ($20 extra) had been cancelled until further notice. They hope to bring those back, but I wouldn't hold my breath. To sorta make up, they were offering two guided tours, one concentratin on the shuttle, the other concentrating on early space exploration.