With the revelation that the _day and _night extensions works on all textures (not just backgrounds) I have started building up a library of surfaces (ie tiles, parking lot, roads, grass, water, etc.), materials (bricks, concrete, roofs, woods) and building facades (ie other buildings that you can use in the background, stadium facades, etc.) I've found that it adds a bit more realism when the other textures darken at night - and there are a couple hundred textures here for you to use.
(Also, if you want to match the darkness of the textures, I pulled the slider down to -57 on the brightness scale in Gimp. I think it helps to have a universal color level.)
You can find the link to the zip file here:
https://drive.google.com/file/d/1Noy...ew?usp=sharing