I am currently playing a 5. 3 campaign, with no invaders or precursors. With 1000 systems total, 224 known, 117 surveyed, I have run across 11 NPR's. All had (most still have) ships. I have conquored 2 them: both had ships at and PDC's on their homeworlds. One was technologically inferior to me, the other was superior. I have found a couple of more homeworlds, but I haven't used active sensor on them to see if there are any PDC's there. Since there are fleets, my assumption is that all the NPR homeworlds I know about have technology and defenses.