Sometimes they can be quite helpful. A pair of moons they were operating on early in a game were extremely rich, with good avail. but limited absolute quantity. The minerals they were providing, especially corundium and duranium, were being produced at a time before I had good mineral capacity to actually get those resources.
I bought it all. Still buying it, actually, even though my resource flow is much healthier--i still burn corundum stocks in about a month of mine construction.