I tend to disagree. There was very much a evolutionary path forward. There were already programs like NERVA in development for an advanced nuclear upper stage.

I tend to disagree. There was very much a evolutionary path forward. There were already programs like NERVA in development for an advanced nuclear upper stage. Once you have that, making the Upper Stage refuel-able, makes it basically into a multi-use space tug for cis-lunar. Then you could evolve Saturn 1B into a reusable Saturn 1C, just like Falcon 9. That gives you a reusable heavy lifter. And it would also safe a gigantic amount of money that was spend on Atlas/Titan/Delta in the next 40 years. The Apollo capsule was not reusable but continuously evolving a capsule design in that direct was certainty possible. But its not the most important part of the system in terms of cost. What really need more development is the lander itself. Making a large reusable lander would have been costly but not really out of reach. You can use an occasional Saturn V for large things like Skylab and special deep space mission. That was a much better path forward then Space Shuttle and ISS.