I'm planning on starting an Inner Perfection game tomorrow night. I keep seeing people who recommend Agrarian Idyll as a second civic. What does it bring to IP?
There are several reasons to get Agrarian Idyll with IP:
(1) It overlaps with the Pacifist requirement of the civic, so you don't have to alter your ethic choice.
(2) It is a very strong perk in general and caters to the typical tall pacifist approach. Your planets have lower max pop counts but significantly higher resource output, so you get the most out of your limited number of planets.
(3) You are incentivised to build Habitats & Ringworlds to create more living space & building slots later in the game, and Agrarian Idyll synergizes extremely well with Ringworlds, allowing you to completely forgo cities on those and just go for a mix of generators & farms.
(4) Inward Perfection has access to the Adaptability tree, which has two significant benefits:
(a) You gain a free building slot unlock, which means you have extra capacity to invest all the extra yields you gain from focusing on resource districts.
(b) You can add a random deposit to each planet once, which is very important since you want to use as much planet size as possible on deposit districts.
(5) The extra amenities from farmers in combination with pacifist's stability bonus allow you to completely forgo amenity buildings. In general you'll have much higher happiness and stability across your empire without any extra investment.
(6) You replace 2 starting cities with 1 farm, giving you a bit of flexibility for early game district choices in your colonies.
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In terms of Research & Manufacturing, it plays mostly like regular games, except that you can stick to lower tier buildings (due to the slightly lower pop caps) on planets and use Habitats in the mid game to do your rare material refining & increased allow production.