Is this just gas?
A while ago I looked at the effect stopping the aperture down from wide open had on pictures and my own little conclusion was that much of the time the cut off point for me was f2.8, meaning that there wasn't a great deal in it other than in the size of bokeh balls from f1.x to f2.x but at f2.8 I could clearly see a difference that mattered to me. Going by my own little test and logic there's not a lot in it between f1.2 and f1.4 or even f1.8 (apart from bokeh balls) and I'd be at sub f2 apertures for only a tiny fraction of pictures anyway.
I have two f1.2's at the moment, an old Rokkor 50mm and a modern Voigtlander 40mm and they're nice things but for me f1.x has only limited appeal. Low light is one thing and the limited dof / bokeh look is another but neither are big deals for me when comparing to f1.2 to f1.4 or even f1.8 apart from the very occasional picture. The one use I have for f1.2 is half to full body people pictures but honestly if I had to make do with f1.4 or f1.8 I doubt anyone else would notice in fact I know they wouldn't. For a pro or serious amateur taking a lot of 1/2 to full body pictures of people I suppose f1.2 makes sense if going for that look and the knowledge it's at f1.2 (not f1.4) but I get tired of the zero dof look pdq. YMMV
The only reason I'm looking at the Voigtlander f1.2's is that although I like the 35mm f1.4 it's funky at f1.x with a messy subject and a more tidy and modern look might be nice plus although the 40mm is a sort of do it all it might make more sense to have 35 and 50mm lenses rather than 35 and 40 which are perhaps too close to justify having both.