Okay here's my inputs.
Coing form the film time to digital, my expereinces with the 50mm f1.7 (used to own this twice) and F1.4 (which I own 1 now).
Basically, by nature of physics, the faster the lens (wider aperture), more light and "stuff that needs to give you great colors" (ok i dun wanna do to the rays stuff in physics).
Comparing a shot with the 50mm f1.7, you will see that the colors are not as "punchy" given a same scene taken with the 50 f1.4mm - even with lengthen exposure time. In the digital world, this can be easily tweaked in post processing. In the digital world, you can tweak and adjust as mush as you want. You can make an image look like taken with a great lens - at the expense of time in post processing of course.
For a period pre-dlsr, I shot mainly slides (provias) and I can see how muted a shot taken with the 50mm f.1.7 compared to the 50mmf.14. This is where you see the need for the faster lens to optimise the image capturing capability to reap the benefits of the rich colors of a media.
Price wise, yes of course the larger aperture ones would cost more as larger glass (raw materials) are needed.
Well eventually, ask yourself, are you a photo enthusiast that have all the time to tweak and alter an image. if yes then the 50mm f1.7 may be the way to go. Gives you stuff to play with in the post processign stage. However, if you are someone who depends on images to make a living then i guess 50mm f1.4 would be the way to go - les adjustment of color richness required.
These days, i seldom do much post processing in colors. Even for casual famly shoots, I would rather save precious time on other stuff than photo-shopping.
Here is a shot that comes out straight out of the camera. The colors are rich as-is. Its wide aperture allows me to take quick candid indoors like this.
