It would have changed the face of power generation at a critical time for climate change if it was allowed to reach fruition. Instead it was locked away in UTC & NASA archives.
An external neutron source does not greatly change the needed enrichment (since any practical subcritical reactor would still need k fairly high, so it is only a bit subcritical.)
The terrestrial reactor and the rocket engine versions are different in how they transmit power from the reactor core to do useful work but not radically so - the core irrotational vortex compressing a high temperature plasma in a single crystal beryllium oxide chamber is the same in both designs and has been tested. The difference is in the cooling gas - hydrogen gas seeded with tungsten nanoparticles to absorb the black body radiation of the plasma for the rocket and water going through a steam turbine for terrestrial power generation.
It would have made some sense to incrementally improve some parts of that architecture (like the Saturn 1B, for example) rather than going down the Shuttle rabbit hole.
The shuttle did make sense for some things it was never used (DoD influence there) and it was an incredible piece of technology. It was also the workhorse for a big part of the ISS. But then again, that all happened in LEO, and different things could have been achieved by just iterating over Apollo/Saturn, in LEO and further away.
Blaming everything always on the congress/president is a way for NASA to never take responsibility. All the success gets credit to NASA but failure is always somebody wrong doing.
Simple changes like not going for hydrogen, separating main engines from Shuttle itself, not using hydrogen on the first stage, vertically mounted shuttle and so on.
The Saturn-Apollo program had a super-heavy lift rocket (Saturn V), a man-rated heavy lift rocket (Saturn IB), a Lunar trajectory capable command and service module, a lunar lander, and a workable wet workshop space station (Skylab).
Congress tossed all of that away. The Space Shuttle program wasn't a bad idea, a heavy lift vehicle that provided a shirt sleeve environment but could support EVA is actually an awesome thing for LEO. But Congress scrapping Saturn-Apollo trapped NASA in LEO because the Shuttle was only capable of LEO. It's not a platform that can support manned Moon missions let alone any more distant bodies.
[0] https://en.m.wikipedia.org/wiki/Apollo_Applications_Program
[1] https://en.m.wikipedia.org/wiki/Manned_Venus_flyby
[2] https://www.wired.com/2013/11/moonbase-apollo-1968/
[3] https://www.wired.com/2012/08/before-the-fire/