One thing I keep thinking on what is the spawn range for NPCs. Some look to scale so they will always spwn even if you get to rank 1k or something. But otherwise any idea on the ranges for the rest (will elite have a chance to show up anyway?).

I don't think elites show up below level 60 from what I've seen. Uncommons however I run accrost constantly. I had 2 uncommons and a rare that I took down last night and 2 more where on my screen when I logged in tonight. This of course is the high end and depends on how much you farm npc's, the more npc's you clear the more chances you have of getting uncommon/rares. I was just knocking them out of the galaxy last night though.

The information your looking for is very hard to determine but it would be nice to add to the wiki. Maybe I'll start taking notes on this as well but I don't know if I can ask others to do the same as it seems to be tedious.