I can imagine that being one of the interesting things that could be added if the game is changed too...in bringing back minerals you have to figure out what/how those ships get built...if you don't bring back metal it's just the same, but does Hayes sell what doesn't get used?  A definite level of challenge to the game can be added if they changed it so specific materials were required for different ships, as opposed to a catch-all RU system that rewards bringing back exotics, radioactives, and precious metals.  Ships made of uranium and gold...would be quite interesting