I got my friend Rachel to be an additional target. You should be able to make out the both of us in the range vs. time plot. We cross paths twice. Here is the original screen cap.
I decreased the time constant in the complementary IIR filter that subtracts static objects from the range measurements. That means that static objects decay more quickly. This seems to have helped a lot in the clutter. I also try to compensate for free-space path loss (signals which propagate further decay). Greg Charvat suggests using the model that the signal decay is proportional to (R^3/2) where R is the distance traveled. Since I'm plotting log of intensity of the frequency components over time, I just add 3/2(log R). Any scaling difference in R manifests itself as a shift. Since I am streaming the spectrogram in real-time, I haven't yet done anything to try to maximize the contrast in the spectrogram. That would probably make the trajectories appear much more clearly.