I'm curious about your experience with how aggressive and expanding NPRs are. I have setup a game with 3 NPR at 150% diff at start, and 28 years in the future, I still have to spot one of their vessel. Are they expanding at all, that's the question. I have surveyed roughly at a distance of 6 jumps in all directions from Sol.
I have met so far the Precursors, another race which is friendly and a third one which was not but was at a tech level under me (so I conquered them). For the 3 others, which are existing as I checked the list of races in the relevant dropdown box in Designer's Mode, I see nothing, and I guess the 3 I have not yet seen are the 3 at 150%, and not the 3 I have seen so far (because I can't imagine that the Precursors are seen as a normal race, and I can't imagine that the lousy aggressive alien I conquered was at 150% diff).
Strange, no? Unless you tell me they could indeed spawn at a distance of 20 jumps from me that is... It makes for a slightly dull game now, although I'm happy to develop a real empire.