that I've made whenever someone brings up reviving the Saturn V. According to NASA, all of the old blueprints and specifications still exist in microfilm format. However, virtually all of the old hands that made the Saturn V possible are dead, retired, or have moved on to other projects, along with their expertise. Not only that, but many of the materials and components used in the vehicle are no longer available, so you'd have to develop new things like avionics and mission software. It's even possible that some of the old alloys are no longer in production. Sure, we could replace them with newer (and possibly better) materials, but that would mean a lot of redesign, retest, and recertification.

The same probably applies for other programs from the era like NERVA. As much as anything, the loss of critical expertise will be a limiting factor for future space exploration. If we wait another 10-20 years before attempting bold exploration like what Bush is proposing, it may no longer be possible without a massive reinvention of the wheel.