No, what they have sounds more like a wall, at best. Most of the times, it's probably just going to be a few systems you skirt around. Pirates/barbarians, on the other hand, actively seek you out, destroying things willy nilly. Few 4X games (none that I can think of, though I think Distant Worlds may have) have just a hyper advanced civ that can't move forward at all, and so is in an inevitable decline.
Star Ruler also had the remnants of an ancient species, which pretty much sat in their systems with huge fleets and were quite dangerous in the earlygame.