It would be interesting if you could trade between the planets that both belong to your faction in the game. Then it could be a tough choice weather you commit to foreign trade or domestic. While domestic trade could be made more profitable but it won't have the positive diplomatic side-effects. In fact it could make other races upset that you are not trading with them. This could also be useful if the minor races are disabled and you are playing one on one. For balancing you could make that domestically only 1 trade route can go from planet A to planet B and 1 route from planet B to A.

To take it a step further, in the future releases with greater diplomacy options, the game could start with domestic trade (less profitable) and then you'd have to negotiate for foreign trade that is more profitable.

What's everyone's views on trade? Does it even need changing? These are just some things that could make trade more interesting.