In my game the goal is to discover all the systems. My first NPR was very hostile, so they had to die. But now I am nearly finished with exploration, but found two more NPRs, one of them is really friendly and likely very low tech level (they don't even have spaceships as far as i can tell), the other one is slightly friendly but surely very xenophobic b/c diplomacy progress is veeeery slow. These guys have a lot of ships though, and they didn't attack me yet, but they make the game very slow b/c pf their ships. I am tempted to destroy them just because of this. It would surely be easier now since they haven't spread out yet i guess.
So I was just curious how do you treat your NPR races in your games? In particular, friendly NPRs? Do you let them live, or destroy them asap?