I can see floyd86's street scene ok, though it is quite dark, and I can see distinct variances in Lynn's posted greyscale. I think the issue with your scene Lynn is that the contrast between the illuminated areas and the shadow areas is not very great. Shadows, and the non-illuminated side of objects, tend to be fully black at night time, or very close to it. I would suggest reducing the Ambient setting on your materials to 0 or perhaps 0.1, which will deepen the darker parts of the image, relative to the lighter parts. I know this can be a pain, especially if you have a lot of materials, but it might be worth the effort, even if only to see the effect it has on the render. You may also need to adjust the % value of the shadows for each light source, if the shadows look too bright compared to the dark side of, for example, the balustrade.
This is just an idea Lynn, I love what you have done so far (as I do all your work) and I look forward to seeing your folding wing solution. After an abandoned attempt at animating a paper plane being folded (collision detection would be nice) I feel your pain!