This has been brought up before, however I think this might be the best way of making it work.
I love the Gas Giants in the game; however I do not like the idea of them being un-colonizable. I know of course technically they cant be, however I believe they should, my reasoning would be like that of star wars, orbital cities. To make them colonizable, I wouldn’t give them population points or even that many logistical points, but tactical points, yes they should get some. I would say that starting off with no investment in them, they would get 0 population, 3 logistics, 10 tactical and no fleet points, since it doesn’t have a population, it would be like a dead asteroid, however the ability to have minimum logistical buildings. You could make this ability to colonize them a tech tree requirement, a higher up tier. This would also bring up my next main reasoning for gas giants being colonizable, Moons! Gas giants have lots of moons.
Moons should be in this game as well. You don’t have to make them rotate around the planet or anything, but have them in the game as minor colonies to planets. You could have colony ships be able to colonize them or if you control the planet first with a moon in system, have in the planet improvement tab, an icon to colonize the moon. If this were possible, I would say they give like 5 population on the first investment then 10 on the second. And they also provide an unlimited metal and crystal income, it would be lower than asteroids, but improving tiers of investment would increase the rate of extraction from them, never exceeding the asteroid extractors. This way of having them as separate entities in the same area of a planet would make for very tactical games, as in a player may control the planet however his opponent controls the moon in the system; this could spark a huge conflict right inside a single gravity well. Terran systems would have a single moon and gas giants could have 2-3, while other planets might have them or not.
And an unrelated thing to the Gas Giants and moons, this game needs Battle Stations. They don’t have to be mobile or anything, but a massive fortress in space that has defensive guns with long range (lasers, missiles, etc..) and fighter bays. Of course it would cost more then building the other structures individually in tactical points, however it would make defending a planet easier to the eye then massing massive amounts of other buildings that clutter up the space around a planet. Instead of having like 12 defensive structures around a planet, you could only have 4 stations.
And that’s my spiel!