Dan,
Bang for the buck is a measure of the usefulness of something versus its cost. And regardless of cost, if the object is of limited or no use, then it will, by definition provide little or no bang for the buck. In my particular shooting circumstances (photojournalism and street photography) for example, I shoot mainly with three zoom lenses;an 18~28 f4~4.5, 35~105 2.8 and an 80~200 2.8, and consider the 50mm lens to be of no use whatsoever. It's not long enough to capture action at a distance, nor wide enough for enviornmental portraits. Its only conceivable use to me is as a low-light high-speed optic. However, this function is performed for me by high-speed slide film (that's film. f....i....l....m. Think real hard and you'll probably remember film), so the 50 sits in the basement with a half-dozen other lenses that are rarely or never used. So I beg to differ that there is no excuse for not having a 50 1.8 or 1.4. In my world there is no reason to have one. But as Uncle Sidney used to say, "That's why we have Chocolate, and that's why we have Vanilla."
If you get a second, take a peek in the Photojournalism gallery. I've got a number of shots posted there, none shot with a 50 mm lens, and I think I do just fine without it.