This is incredibly low priority but what if the surface of the planet around your buildings slowly became more "mechanized" similar to Zerg creep from starcraft. It would have no game-play impact but would make the players impact on the world visible in a much more aesthetically pleasing way. It would fit the fluff for a self-replicating resource hungry race of machines. An even more advanced implementation of this idea could be power conduits and mass conduits routing from power gens and mexes to factories to give your base a more "functional" feel. Might kill your graphics card though.
I actually had the same thought a while back. As you say, no gameplay impact and low priority, but a cool way of conveying your army's corrosive influence on the planets you conquer. Perhaps this is how the metal planets came to be? Originally normal worlds, eventually completely consumed by nanotech. Depending on how large the mechanized areas are allowed to grow, they may have a small impact on the intelligence game - if you see metal, an enemy base is nearby.
Well they already have Tarmacs and such for some structures, I don't imagine it would be that much harder to expand that into what you're thinking of, I'm just not sure that 'mechanization is really the right term, but then again whenever I hear that I think of GaoGaiGar so go figure. Mike
