[Baron Munchausen]

Sure, building a ringworld or sphereworld should affect the planets in the system. You should have to destroy them before you build either! These structures are actually quite fragile and any planets or any extra mass in the system at all would make them very unstable and prone to breaking up. The current method of constructing them is a sort of 'quick fix' way to cram a much wanted feature into the game. If it were done properly you'd have to destroy all the planets in the system and then the asteroids would be 'used up' in building the structure. Then, there would be a new background image. Neither a ringworld nor sphereworld would fit in a single sector! They could be really, really cool images, though. A ringworld or sphereworld should be 6 sectors across or more.