Now this water world, and this new information, might change that. It's way out orbiting the B star, and game forced me to use one of it's two orbital slots with my primary port, with is a commercial outpost. If the population increase only affects things orbiting the water world, I'm not sure if replacing one of those T3's I was planning to build and building it instead in the 2nd slot would do me much good. However if it affects the whole system, that might be different. Thoughts?
Population is mostly just a number on the map. Apart from making the BGS waaaay more stable (or increasing effort).
What population offers is huge supply and demand, and therefore goods and possibly good trade routes.
After we have built several T3s in our squadron, our current approach is: only build T3s for population boost around earth likes/water worlds. There is no need to build a T3 anywhere else. A well built T1 offers significant resources (see
Victoria Wolf Composites Market ). A well built Coriolis offers more supply that can possibly be drained, except with a CG ( see
Victoria Wolf Steel Market ). The T3 is the difference between double-triple digit kilotons supply and megatons supply. A good system will make a T3 meaningful through weak links. ( see
Victoria Wolf Resort Market ). Victoria Wolf Resort, my Tourism station around a waterworld, offer triple digit kilotons Steel, Aluminium, Titanium, etc. With 20% Refinery economy. And that's after only 4 population ticks and
118m pop 223m pop (Edit: pop ticks have been updated, and the system is now in Boom, which changes the demand/supply figures, but the point is still valid). You do not need more. You do not need megatons. (Edit: At least there is no use case i can imagine outside of a CG).
So for resource supplies i'd concentrate on T1 planetary and T2 Coriolis. Everything else is megagrind and unnecessary overkill. Sure, an eternal construction to get rid of your T3 points. But who knows, maybe keep them and put them to yet unknown uses later.
I'd place a T3 around the WW, and rather colonize another system than build an additional T3. You get an amazing system for 200k. With 4 T2 economy buildings, security, standard of living, a T1 port and a Coriolis. One that supplies a 40-60ly radius, 500ly if it's good for carriers.
But that's just me. If you have emotional or flavor aspirations, build all those T3s.