I added basic output to do ngspice simulations from within KiCAD v5. Turns out it can all be embedded in the schematic. It doesn't do MC yet, and doing so isn't hard in ngspice (there's an excellent example on page 430 of the ngspice manual; basically use the scripting frontend command 'alter' to change component values and rerun the analysis, outputting plot data each time through, repeat a statistically significant number of times) - but I need to make sure it works correctly from KiCAD. This is pretty neat, because the schematic can be left as is and the nominal E values with a gaussian tolerance distribution are then repeatedly set inside the loop. The original baseline can then perhaps be plotted in a different color or stroke to make it stand out... need to experiment with this.
I also made it output Bessel filters with the smallest Q first (doh) and front load all gain in the first stage for any cascade. There's no reason not to for simple, uniform filters like this.