I do see the problem with these, but making them only patrol to the planet next door would make it kind of pointless. The risk/reward is that if you wake it up before you're ready to deal with it, it's going to spawn lots of gatlings that are hostile to everything, and they will start chewing their way out through the AI worlds and into your worlds. Just a few of these guys can really wreck your defenses in the early game. That said, I did manage to befriend one in a recent game with only about 3 planets to my name at the time, so it is possible if you blitz the command station on the dyson planet early and then pull back everything you have to defend your home command station. (I lost every other world, but still) That risk paid off in a huge reward, because I now have between 50-200 gatlings on every single planet (X map and fallen spire, so skipping worlds is kind of pointless). If nothing else, I would love to see their numbers decreased. If their power should stay the same you could increase their power and hp proportionally to their number decrease, but they are really slowing down the game when I have to move in a big fleet to a planet that they're also patrolling.
I'd just hate to see the sphere turned into a pointless part of the game that no one uses, and I think having it only visit next door worlds would do that. Even in a small 40 planet map that will quickly become irrelevant. Giving it a chance to remain neutral would also make it unusable. Those gatlings are TOUGH. If you didn't have a way to make them friendly, you might as well end your game right there. Once you wake it up they'll just be plowing into your worlds and eating your resources for the next 5-10-15 hours. There's nothing fun about that!