Reduce maximum colonies to just 1. For me this increases attachment: I like it when I can think of the colony as "my home".
Not with the way colonies work now, with colony limits. Having five is enough to get what the player needs to sustain his faction in case of a bad planet seed.
Also, player can just pick a primary world among his territory and use it as his home base.
Make colonies on planets other than terran planets more viable. Right now it feels like a terran planet colony first is almost mandatory.
Thanks to how colony items work, habitables are generally less useful than non-habitables. In particular, "No Atmosphere" planets are very valuable, you need one to use synchrotron to produce enough to feed your Military Base/High Command. If you want to use Hypershunt Tap, you need Catalytic Core too, and that requires no atmosphere to work. But you still want one or two habitables for Farmland, Organics, and maybe a place for the Biofactory Embryo.
While lower hazard is better, anything at 200% hazard or less is fine.
And if a player simply wants a colony or two that never grows past size 3, then a non-habitable is better because growth will not be positive. With a low-hazard habitable, it will have growth, and it cannot be stopped from growing bigger in time short of removing the spaceport.
Make the colony play a role in the upcoming late game content. Having a colony is something that should be required to do the late game (and you'll not have to be as picky as before and find a good terran planet, any good planet will do).
Yes, there should be problems that are beyond a single fleet to solve. With fully grown colonies, the player has the resources to build up a military and use it to do strategic things, like conquer and occupy some core worlds, or attack and kill a planet-sized monster.
