Apollo was a dead end. It had been designed to reach a single goal, in which it succeeded beyond expectations, but it HAD no follow up program. There was NOTHING waiting in the wings to build on the success. In order to have the glowing future of bases on the Moon, Mars & large permanent orbital bases the follow up program would have needed to be sold in the mid-'60's. Nothing was even shopped. Without the USSR showing any interest in reaching the moon once the American's won the race, the political will simply didn't exist to keep drilling holes in the sky. It was a tragedy, but it was also just about a certainy.
The shuttle program, had NASA gotten what it originally requested, was the next logical step. It would have allowed for the construction of a true orbital base. Without such a base, it is nearly impossible to see how a lunar base, much less a Martian habitat, could be maintained at any reasonable cost. The Shuttle program, as originally laid out, would have had permanent bases on the Moon by 2000.
Unfortunately, NASA got Congress' version of the Shuttle since they lacked a sufficiently powerful sponsor in the Senate & House to get the full version built. Congress saaved some bucks (Of course it also killed two crews, but that's okay, none of them were related to members of Congress.) and NASA figured it would go back & get the full version, with an updated orbiter, in a few years. That, as we all know, never happened. Now, we are going to toss everything we learned from the shuttle into the dustbin & start all over.
Can anyone say "failure"?