It changes all the time for me. Sometimes I get ten shots on a roll that I really love- other times I can shoot for weeks and not produce a single thing worth printing. Street shooting is one of the toughest things to do well- it takes a lot of work to make really good images- they don't just happen. Even if you are witnessing something incredible and wildly compelling visually, it still takes work to make great pictures.
I used to be a second shooter for a wedding photographer who would give me a roll of film, and tell me to get 36 images that would all end up in the book the bride bought. I'd shoot stuff that I thought was good, and we would sit down and go through it later, and he'd critique me every point. One idea he kept impressing upon me was this: each time I brought the camera up to my eye, think- is this shot worth making? Is this THE shot? Can I make it better? How? How compelling is the sujbect? Is the timing right? Am I in the right spot to get the best shot? Am I making the technical choices correctly? Should I get closer? Back up? Change lenses? One school of thought is "film is cheap, so shoot the hell out of it, and edit for the good shots later". But on the other hand, consider each shot? Is it good enough to click the shutter?
I notice that often times when I get near the end of a roll, I slow down, being more stingy and careful with my film- especially in the think of action. I don't mind the Leica's bottom loading, but the M3 is a little slow, and I don't want to miss anything. So I save my frames for ones that count. As I go on, and get older, and gain experience, I shoot less, and get a higher percentage, but I'm still always trying to balance the opposing philosophies of "film is cheap, so shoot" with "wait for the best shot, then nail it."
I can say one thing- and this is the point that made me dump my motor drives: most of the time, if I shoot a bunch of frames of a situation, I will get at least one that is ok, at least usable. But when I only shoot one frame of a situation, it usually turns out to be because I got THE shot with that one frame. I can feel it when I'm shooting. If I don't get it, then I keep burning film, trying for it. But when I get THE shot, I know it, and I wait for the next one. This is a beautiful Zen moment in photography, and I am always looking carefully for it.