While very early work on Apollo was underway even before JFK took office, his pledge to land a man on the moon before the end of the decade (nice diversion from the Bay of Pigs disaster) and his subsequent assassination made the goal of landing on the moon an end in itself. NASA funding peaked around 1966, with the peak budget being roughly $30 billion in today's dollars, about 5% of the total federal budget for that year. Adjusted for inflation, NASA's budget had pretty well gone down every year since.

While NASA people like von Braun dreamed of going beyond the moon, no president or Congress has authorized any such thing. That made the Apollo program an end in itself. Once we'd succeeded with Apollo, it became a dead end. Even some of the NASA flight directors were happy to see the end of Apollo 17 before they lost another crew.

It's hard to see it, but the Saturn V was the minimal vehicle capable of landing two men on the moon for up to a 3 day stay. There were proposed growth versions of the Saturn V but none got past the study phase because none were funded. Had Apollo been allowed to continue, those growth versions could've allowed much more ambitious lunar missions and better technology.

I base my views on more than 30 years of studying aviation and space history, as well as several years working with military space systems. Experience has shown that doing something right is expensive and time consuming, but cutting corners, especially on testing, is even more so. I'm not at all opposed to sending humans to Mars, but my study and experience has convinced me that we're not nearly ready. Applying the lessons of history, both of flight and space systems development, shows that overly ambitious attempts to rush development of technology usually ends in failure (Apollo 1, NASP, X-33, anyone?)