The thing that NASA got right in the 1970s is that reusability is the key to reducing launch costs. It's hard to lower the price of a pound to orbit if you have to buy a new rocket every time you want to launch something. The Space Shuttle was originally designed to be an entirely reusable system, and was sold to Congress and the public on the theory that each orbiter would be flying several times a year and have a turnaround time measured in weeks.
Problem is, the shuttle as implemented wasn't actually meant to do any of that. It was meant as a jobs program for government engineers and technicians. It was not capable of flying again after a mission until it had been thoroughly inspected and had its engines overhauled; usually the heat shield had to be completely disassembled and repaired, too. Instead of a turn time of a few weeks, six months was not unusual, and at the cost of a billion dollars per flight the platform was anything but cheap to operate. (And its safety record was less than stellar, I might add, since we lost one in ascent phase and another in descent phase--two catastrophic losses out of about a hundred or so missions flown, which is considerably less than enviable.)
NASA tried to do too much, too soon with the shuttle, and they did it wrong to boot by trying to design everything from the top down. SpaceX is doing it the right way: build it, fly it, break it, fix it, fly it again. That paradigm is mentioned (almost verbatim) on their web site.
Trying to make the jump to 100% reusability from 100% disposability is impossible. No part of the Saturn V was reusable; it had not been designed for that and the entire vehicle was built to be used one time only. The platform could have evolved into a reusable design, given time; upgrading electronics, adding parachutes, making other incremental changes and testing them with each new flight exactly the way SpaceX is doing.
Okay: when the Soviet Union put Yuri Gagarin in orbit, they did it with a rocket that had evolved from an ICBM design. They didn't work out how to build a V2, fly it successfully a few times, and then decide it was time to build a Saturn V. They took the knowledge they got from their German rocket scientists and built on it, and evolved a design for an ICBM...and then demonstrated their ability to hit any point on the globe by putting a man in orbit around it.
There is such a thing as being too ambitious.
It is possible to build a completely reusable system that will reliably get people into orbit and safely return them to Earth's surface, but we're not allowed to skip any steps in the development of the capability. Knowing that a thing is possible is the first step on the path but it's not the same as knowing how to do it.
However: it's also true that the shuttle program taught us a hell of a lot about what not to do when it comes to building spacecraft. In that context it was probably necessary that we make the attempt, even if it did set back the exploitation of space a couple of decades. The biggest issue was how hidebound the entire program was: at the time of the shuttle system's retirement it was still using computers which were designed using 1960s technology, and which could have been replaced with single-board systems if NASA had been capable of making such changes in anything approximating an economical fashion.
There was no money in the program for hardware upgrades. There was certainly no money for documentation changes, which was the biggest obstacle to changing the hardware. Installing new computers, for example, would have meant revising a great deal of technical documentation and recoding all the software--which was economically impossible given NASA's inability to garner a budget which was much more than about $20 billion per year since the 1970s. At a billion dollars a flight each shuttle mission itself was an enormous drain on NASA's resources.
(Side note: a single Commodore 64 has more computing power than the entire shuttle orbiter. I'd wager that a computer with an 80286 processor could have emulated the shuttle computers in real time, thus enabling NASA to continue using the same software library. But--again--money, for testing and documentation and-and-and. Yeah.)
I'd wager that a lot of the printed documentation for Falcon 9 is full of temp rev pages--yellow sheets inserted into 3-ring binders full of schematics, parts lists, and descriptions--and I'd also expect they have teams of tech writers who do nothing but churn out temporary revisions for the manuals. FAA regulations require it; they do not require that the manual be revised every time a change is made because that's f-ing impossible but you can't service a piece of flight hardware with an out-of-date manual. But of course there will also be on-line documentation which can be updated a lot faster and more easily (and features virtual yellow pages because the FAA requires that temp revs be printed on a specific shade of yellow paper. "Canary", for the record).
Man would I love to be on that temp rev team.
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In the "alternate history" story I wrote about a NASA rocket engineer who becomes an astronaut, I--if anything--am too pessimistic about the advancement of rocket technology given an unbroken string of Saturn V launches from 1969 onward. It's a world where the politics worked out differently (Nixon let himself be impeached, among other things) and the commitment to space exploration was politically impossible to abandon, so we kept on sending people to the Moon and we kept on flying the Saturn V. At the beginning of the story, an upgraded and uprated Saturn V (referred to as "V2.0" by the main character) has recently gone into service and is having some teething pains, and it's his job to figure out why. But since the story is set in about 2008-ish, the upgrade to the platform is actually taking place a hell of a lot later than it actually would.
The Apollo program had originally been meant to fly three more missions--18, 19, and 20--and after that it's likely that another program would have replaced it. Still, I'd wager that if it's politically impossible to cut a program like Apollo, it's probably politically possible to extend the program and ask the various contractors to spin up the assembly lines: "Guys, we're going to need at least another dozen of those things...."
So, what the hey.