I'm sorta reminded of Dune 2(000) here. It allowed you to order untis in bulk at a spaceport. You got them all at once, and at variable market prices (sometimes nice and cheap) but you had to wait quite a while to get them. It didn't detract from the game at all. Just waited a while and it told you the shipment had arrived, and they all pile out of your spaceport.
Granted, the above idea doesn't quite work here. But I can see it working with the mining trips. Send a ship off to mine, and wait until it returns with a large pile or rare resources. You'd have to spend money to prepare the ship for launch, and you'd be without the use of the resources you put into it while it was in transit, but after a while when it returns, it should hopefully pay itself off. I guess you can even throw in a chance of a disaster taking out your ship.
That idea for winning a round that Hacker suggested sounds like it could work nicely.