They are enough to provide a significant navigational hazard (especially at the kind of velocities in GC2). A good example would be they Kuiper or Oort belts in our own solar system.

When travelling at a high fraction of c, pebbles are probably a bigger concern, both because there's more of them and because they're much harder to detect.

well, that's why there's stuff like the "Q field" that gets described in one of the hull tech descriptions...

most of the tech work of making larger hulls, according to the descriptions, isn't in how to build the hull, but in how to keep it from tearing apart while at speed.

also, i can easily imagine that the warp (or whatever) field around a hull would encourage small obstacles to part in front of, flow around, and then come back together again behind the ship. yeah?

in this case, it would be the more massive obstacles that would present the bigger danger.

although, i can imagine that a nebula might be a hassle too, if it reduced sensor range... that would require ships to slow down, like automobiles in a fog?

but in any case, as the original poster noted: the trouble isn't in implementing map terrain in an interesting way, but in making sure that the AI players can not only cope with the new feature, but also use it to their own advantage against the player!