One of the main issues I find with Prosperous Universe is that a lot of resources when you use them vanish in thin air rather then being able to be recycled. This problem becomes more apparent with more and more systems being added that requires players to upkeep buildings, planetary structures, and population infrastructure.
The degrading buildings can’t be recycled for scrap metal, the water that is consumed by workers and farms can’t be renewed. Food consumed and ejected can’t be turned into fertilizer.
In real life recycling is used because it’s much easier to recycle a material then dig it out of the ground, especially metals.
It would be good to have buildings that recycle materials at various levels of efficiency-for instance having farms and workers output, “dirty water”, “sewage” that would need to be processed.
It would also add a bit more life to planets as you’d want another company that specializes in that rather then wasting area on recycling buildings.