So interplanetary nebulas aren't a real thing, since real nebulas are way bigger than that, but I think having big (bigger than planets) colorful clouds would still be awesome.
They could serve purposes such as:
- prettying up the place (because colorful clouds in space are nice)
- environmental hazards (limited scanner range, limited visual range, "acid" damage to the hull or "ion" damage to the systems, disabling of ion thrusters, gas explosions when firing weapons)
- atmospherics through sound (hearing the ion storm rage when inside the ship) and nice particle effects when inside
- information about far away ressource locations. don't need to render asteroids, just a single relatively low poly cloud
- in tandem with environmental hazards, there could be rewards for exploring/harvesting in dangerous zones (higher ore density/derilict ships/emergency beacons)