Order events

A random order event where some factory or vendor asking for a number of specific modules to deliver, and then gone once you fulfilled it (so you can build something, and then delete it). You could get some interesting reward, like an extra resource node what you can place wherever you want, or some kind of currency which lets you buy the same, just you have to complete more of them to gather enough to buy.
You could have up only one event at a time, and it would stay until you complete it. Then once it's done, after a while you would get a new one.
This would keep the game fresh a bit and wider, instead of being very linear.