Update... the massive overspawning doesn't just happen in a downtown Wasteland area, it seems to be anywhere in the Wasteland at night if you stick around one place for 10ish minutes.
I just found a nice isolated building away from everything, and as I looked it over more and more friendly and enemy NPC's have been spawning in and now there's a small army around my potential new base. It'd be cool if my FPS wasn't in the 30s 
There's not *as* many enemy NPC's spawning in as downtown it seems, but there's still far too many and I can't imagine how horde night performance would be.