So, that would be an awesome project!
Why are you not using this through KiCad? That's what I would expect an amateur to do; especially since they handle the UX that you are complaining about.
And you are complaining about tangled code but that code is almost certainly hyper-optimized since performance actually mattered a LOT to people running spice simulations. ng-spice (and Spice3 and Spice2) were not written for programming ease; they were written to get a real job worth real money done.
In addition, any change you make to that code needs to be run back through numerical regression tests to make sure you didn't break things since this is software that people expect to get correct answers.
However, if the legacy seems to bother you so much, perhaps you should look at Xyce from Sandia?
They sound like an amateur at circuit design, not software engineering (which is how I'd describe myself too).
The original point stands. Ngspice shows its heritage from the days of Fortran far more than a modern code base would or should. It's sole great virtue (from my point of view) is that it integrates with KiCad and only falls over with no reason about 5% of the time.
I would suspect that some of the simulation systems coming out of the Julia community or Xyce would be a better base.