One normal to moderately wide lens works for a good chunk of street photography, but far from all: for example, not for the longer shots in Michael's recent essay. Substantial cropping is about equivalent to using a substantially smaller sensor: more IQ loss than the lower speed of a zoom, I suspect.
Right now, my fantasy for a small, discreet kit is a small Micro Four thirds body with in-body IS, articulated LCD (no complaints about LCD washout with night photography!), the promised Panasonic 20/1.7 "wide normal", and a smallish telephoto zoom. Camera motion is far more of a worry for most of my photography than subject motion, so several stops of stabilization is worth far more than a lens that is several stops faster, given the weight, cost, and shallower DOF that goes with faster apertures.