Carying the two more plausible suggestions over from the other thread, as suggested:
1. Installed installations. It is a bit irritating how everything in the Aurora universe seems to be portable, even a factory that was in use for the last few decades. It might be a nice Idea that would add even more need for planning to put installations into a "storage" after being constructed, where they don't have any benefits. From there, they could either be transported away or installed on the planet. Once installed on whatever planet, they bring their benefits, but cannot be removed again.
2. Power. We're running into a real life energy crisis currently, yet so far no 4x game has wasted any thoughts on power. Make power a resource and you will have immediate benefits in terms of complexity all over the board: More installations that must be built, one more factor to balance, and more stuff to research. Might even be coupled with special resources for advanced powerplants.