My other suggestion would be to make rail require the use of metal to build. This would drastically increase the cost of building a rail supply system, perhaps prohibitively so on metal scarce planets. I certainly wouldn't object. My one main gripe with the game so far is that I feel that resources are still a bit too plentiful and that I want to feel a bit more, I dunno, like I'm needing to fight over them more. I found Distant Worlds was at it's best when resources were something you really had to fight over
