Okay here is an update. I did the Shadow layer over to make it a little larger. Not sure I like the sharp curve in it, but it doesn't look horrible. Also took Ascensions advice and remade the City Lights layer with a smaller brush. In fact, I varied the size of the brush* from area to area.

* Gimp Paintbrush tool using the Sparkle brush at 45.0 Opacity. Set Random to Opacity, Hardness and Size. Varied size from 0.04 to 0.10. Also had Fade Out set to 100, though I doubt that had much impact.