Based on this image by Munashichi: http://www.pixiv.net/member_illust.php?mode=medium&illust_id=13322496
I think I'll call this done. If I were to try and fix the bits that bug me I'd probably end up re-doing the whole image.
Blender 2.6x (Daily builds)
GIMP 2.8
Render time: ~2h 30m
Samples: 500 (Although I could have lowered it without losing quality.)
Full resolution: 1,920x1,464 (not power of 2, whoops)
Vertices: 318,224
Objects: 938
Lighting: 1 Sun mesh light; Ambient Occlusion at 0.05 and distance of 1.000.
The emission of the street lamps is too weak to affect anything apart from itself.
Foreground shadow is caused by a large cloud object with a translucent material. (I don't know if it actually does anything having the material, I just have it because it made sense.)
Clouds were painted in GIMP.
Image was composited in Blender.