240Hz or not worth it
Only half kidding. 240Hz is the only refresh rate next to 120Hz that can accurately reproduce 24/30/60 FPS content.
Hmm, curious why you would say this. With 24p and no frame interpolation, all you need is 3:3, 4:4, 5:5 pulldown and you're done. Perfect 1:1 repro of 24p due to integral multiples of the (fixed) source framerate.
If you want BFI then you need 2X integer multiples avoid interpolation, so, 4:4, 6:6, 8:8. Or, in other words, 48hz x 2 = 96hz, 72hz x 2 = 144hz. 60hz / 120hz won't work, obviously, but 120hz does work as you say because it's 5x 24. 120hz is indeed a "magic number" which is widely compatible with 24 / 30 / 60hz native content, as is 240hz / 480hz / 960hz.
To me the big ones are 24p and 60p, and I use FI instead of straight up frame repeating aka 1:1 pulldown ratios.
Have you tried Dmitri Render? It hasn't been updated since 2015 but to me it looks way better than SVP, hardly any haloing artifacts which I find extremely irritating in SVP. I wonder if D.R. just gives up if the motion vectors are too complex and just says "eff it", like some TVs do. I watched Rogue One on D.R. last night, best space fight scenes EVER! And D.R. looks insanely good on my G-sync monitor too, at 144hz. My projector lamp died so I've been having to watch more on my G-sync lately. Man, D.R. is good. Way better even than my PJ at 72hz / 75hz.
I haven't done too much research about 75hz over 72hz (or 71.928 rather) mode on my projector in terms of final interpolated image quality, so I'm wondering if indeed 75hz not being a multiple of 24hz is a good thing or a bad thing. Do I want most frames to be interpolated? Or do I prefer to have 1/3rd of them be straight-passthroughs. This engenders questions about 24p source frame motion blur, is it better to apply de-blurring (which will introduce some artifacts but sharpen up frames) prior to any FI filters or leave it alone.