I don't know if it's feasible to have structures that produce partial units of resources, but researchable or ct lab discoverable 1 space, .5 production buildings would be nice to fill up the few leftover spaces on invulnerable planets that can't benefit from the 2 space attack/defense structures or the 1 space population structures. If that's too powerful, then 1 space .25 production buildings.

Just to be explicit, I'm thinking of the following buildings:


I have no idea what a reasonable cost would be for these, so suggestions for cost and other improvements to the idea are welcome!