Imperator Fyron said:
"MOO2 had space monsters. That speaks for itself. 
Sometimes, random wandering space monsters would attack a system. Or even the dreaded Antarans would send a small force to wipe you out (or an AI empire)."
Ah yes, but GalCiv in the OS/2 days had the Ominarians. They were a nasty genocidal race that always declared war on everyone, and could reappear, even after they were killed off. In GalCiv it was so worthwhile to have a buffer zone against them that I'd even gift weapons tech to the aggressive races (making sure I had slightly better tech, of course)
You can't really gift the Sergetti some weapons as a buffer against the Rage, for an SE4 example. The Sergetti won't take it, and there aren't make or break techs in SE4. And the Sergetti are sure to turn on you as well as the Rage. So these diplomatic tricks aren't part of an SE4 game. Meh.
'Couse the Devnull mod
has space monsters modded in. So there's another SE4 strength.