EDIT: Lost over a million people (1,634,668) on my home planet that turn. Realised that my Quatloos had disappeared so it couldn't have bought food like Dave said it would, likely from all the buying of Food and Steel that it's been doing lately. Put tax rate up to 20% so I can get some cash in. That also means means Long Range Sensors are much too expensive for what they do so I've scrapped them. Next turn I'll build loads of Blackbirds to cover the rest of my PD range around my home planet (like I've done with my secondary main planet).
I scrapped sensors on my home planet a long time ago. They're useless once you have a ring of planets around you that are lower population and therefore cheaper to build sensors on.
Rule of thumb: sensors and PDs should, ideally, be built on low-population planets, as that causes their actual expense to remain low, while their benefits are the same. Ultimately, such upgrades on home planets are maximally inefficient if any other option is available. Building a colony right beside your home planet then mind controlling it at 30 society just to build sensors on it is probably more efficient than building them on your home planet.
