As with 'bokeh' 'nifty fifty' is a term that didn't exist when I started taking photographs. A 5omm lens was what you got when you bought an SLR camera. It was considered to be a 'standard' lens.Today the 'nifty' seems to have gained a cult following. Perhaps this is because it provides a cheap way to get a fast lens and the 'bokeh' effects that come with that territory. Fine if all you are interested in is getting soft backgrounds for the sake of having soft backgrounds. Whatever happened to 'f8 and be there'? I choose a lens by focal length to make the photos I want to make. There's no point having creamy-dreamy backgrounds if you can't frame the shots.
For some time I've had a 24mm almost welded to my crop sensor camera. The image quality may not be all it could be, but it makes good photos. Prior to that I had a 35mm which had better IQ and also made some good pictures, but not as many. I found the focal length neither here nor there for most things. Odd as it equates to 52.5mm on 35mm film and I used to manage okay with a 50mm on my Pentax. So I picked up a f1.4 'nifty fifty' to see what difference that would make.
As an alternative to the 24mm it's an improvement over the 35mm. It does require to adjust how I see though. For walking around the two lenses provide a nice compliment to each other and make different photos. I can't say that the faster aperture bothers me much. There's not a great deal of difference between the out of focus effect at 1.4 and 2.8. It's noticeable, but in most instances it wouldn't bother me. With the ability to use higher ISO values with digital than film there's no advantage to be had there as there was with film. For me it's speed is certainly no reason to choose the lens.
Why not use a zoom? Simply because a fast zoom, I have one which covers the same range and more, is big and heavy. With either of these lenses on the camera it's light and unobtrusive. The spare lens can also slip easily in a jacket pocket. Of course, I can use also use the same lenses on a full frame digital. And when I do fit a zoom one of these primes can go along in a pocket keeping me mobile (I hate carting a camera bag around) and giving me extra options.
The 50mm will also have a place as a fishing lens. My travelling light kit can now consist of the two primes and an extension tube - the fifty plus a tube does a good enough job of close up work. It's a pity I don't have a teleconverter that will fit it too.
Should the 'nifty fifty' have the cult status it seems to have? I don't think so. It's just another lens that does a job or two. It doesn't work magic.