It's always fun to be a Monday morning quarterback. Especially when it comes to engineering. Ambivalent Engineer, Chair Force Engineer, and Selenian Boondocks do it in oodles this past week.
Maybe a Harry Turtledove book is in the works?
All joking aside all this "what if" business reminded me of another engineering "what if" from another industry.
In automotive one of the laments I've heard concerns Ford continuously discontinuing lines of automobiles that are otherwise successful, but at the first sign of trouble they panic, ditch and run.
The old Ford Taurus is often mentioned as an example.
Compare that to a Toyota Corolla, which is the same line of car, but it's been around so long that it's benefited from incremental advancement in efficiencies and design. You can see a pattern developing about why foreign auto makers are beating the heck out of north american manufacturers lately.
With the little engineering knowledge I have compared to the three engineers listed above, I can see the biggest problem with NASA when it comes to space vehicle development is that it abandons too quickly a design when it shouldn't, and doesn't do it quickly enough when it needs to.
NASA could have easily decided to run a downgraded Apollo program based on the same tech, and engineering. Instead they went back to the drawing board and started from scratch. Otherwise, as mentioned by Ambivalent Engineer, they could've chosen a path that would have benefited more from the expertise, engineering, and technical achievements of Apollo.
That being said, as Selenian Boondocks points out, it's precisely that line of thinking that lead NASA to want to keep as much of the original Apollo team of engineers in the first place. Because NASA wanted to do this, they ended having to make a whole bunch of technical decisions that almost eliminated the value behind keeping the original Apollo team together in the first place as I see it.
With the Space Shuttle, one wonders why the program was continued as long as it was. Perhaps it was faith that with incremental advancement the program would eventually prove viable.
In the end the decisions made, were the decisions made. It's useless to debate what could've been different if doesn't lend clarity as to what decisions we should be making today.
In short, as I see it, the effort to build a national space plane was a complete and utter failure. A system much more like Apollo would save money and be safer. NASA's current CEV program reflects that, while trying to keep as much of the original Space Shuttle engineering valuable.
Again, that's how I see it, with the limited engineering knowledge I have compared to the writers above.