> Makes me wonder if a solar system wide civilization, with trillions of beings, wouldn't invest in ships to go to the next system, extract resources, and create a stream of resources ships going back to the original solar system.

This reminds me of those old 4X-type games like "Stars!" where I would often do exactly this. Basically some planets were good for living on and others were good for mining and you'd have a constant caravan of freighters from the latter to the former.