If one is "speed happy" then that is that. I was a professional photographer over a 50 year span and never owned a 1.4 lens. I did borrow a 50mm f1.4 lens from my employer and shot a photo at f1.4 that was used in Life magazine. Now that I am retired I do happen to own a 50mm f1.4 Nikkor which I bought for approximately nothing. Swell lens. I won't lecture here about owning too much gear as I probably have 100 film camera bodies and lenses. But I'm getting rid of all my Minoltas and keeping my Nikons. Well, I may keep a Minolta rangefinder or two, but no film SLRs.
Having had a pic used in 'Life' and owning that much kit, you are operating at a skill/quality level and, I might add, quantity (100 bodies and lenses!) that I could never aspire to. When I get another lens, it tends to be 'instead of' rather than 'as well as'. The only addition I'm considering is a longer lens, a 180/2.8 or 300/4, mainly to take pics of my dogs.
I has been argued that f1.4 lenses are simply no longer necessary - sensor quality at high ISOs being what they are. I tend to agree with the logic but, then, it's not all about logic.
I had an AF 50/1.8D which was a perfectly good lens and I quite recently swapped it for an AF-S 50/1.4 G. The AF-S lens is bigger and slower focussing (although maybe a touch more accurate with it) BUT it has a look that I love and I use it at 1.4 very often. I think it is a under-rated lens and I'm very happy with it.
However, and this discussion has been touched elsewhere, there is more to lenses than the mathematics and you either like the 'look' certain lenses bring or you don't. You are far more experienced than I am and you may well be able to quantify it better but the nearest I can get is a combination of the bokeh, the colour rendition, the rate at which the OOF areas actually go out of focus and probably a couple of other things. Leica M glass has it, my AF-S 50/1.4 has it to a degree whereas the 50/1.8D didn't and my curiosity regarding the 58/1.4 centres purely around these qualities. We are told that the 58/1.4 was designed to prioritise 'look' over 'sharpness' and I'm curious to see to what degree they succeeded.
Open a thread asking for examples from the lens, here and on other forums.
When this lens first came out, several buyers returned theirs and asked for different samples. There must have been some sample variation, at least with the original batch. I would check around.
If this lens had been F1.2- I could see getting it. I'm a "Bokeh Fanatic", and a "Fifty-Fanatic". I just could not see paying what Nikon was charging for this lens. Of course I spent an Equal amount of money on the 1949 Nikkor 5cm F1.5... which was Absolutely Worth It... and will probably long outlast any new AF lens.
I have seen examples of images from the lens here and elsewhere but to draw any meaningful conclusions I think I would have to have one and use it.
Interesting about sample variation - but I think that's more common than we sometimes assume. From reading tests on the AF-S 50/1.4 and comparing their conclusions with my own, I think I may have been lucky and got a good one.
Value! Aways difficult to quantify. My attitude is that if a lens has something that you like, or need, or fits your way of working better than the next best lens then it is 'worth' it. It's a matter of do you have the cash available or will it ever make it to the top of your priorities list...
For me, unless I go back to my old job, I will never have that much cash available because no camera lens will never make it to the top of my priorities list! However, I do like these discussions and I may well hire one at some point - just to scratch the itch.