No need to go nuts.Remember the Death Star? It was said to be the size of a moon. One of these could conceivably mass produce those. Or build larger things.
I read a book recently about such a system. Dyson sphere, weird machinery on the inside. Planets don't have any intelligent life-forms. The ancients built the sphere and went into a sub-dimensional pocket isolating themselves from the rest of universe.
Then two forces arrive and start battling from the system...once the intensity is hot enough, the ancients get angry and come out from sub-space...
This sort of thing would certainly add flavor to the game, but is more of an 'icing' than 'cake'