I have been saving up my power crystals every day now because I don't really have a lot else to do at the moment and the power crystals seem to be the only things that really make auto sales because people are probably making new mines with power crystals instead of spending upx directly on new mines.
With all of that said, I do lack colonies, moons and planets as the majority of my mines are base mines that I built just to work everything into the game.
I guess I could start burning power crystals daily and making a bunch of moons. I don't love the idea though because I'd rather have excess crystals to sell but if I dabble in the making of planets I might be able to snag some auto sales if and when people actually do buy mines.
Either that or maybe I can get more people to attack me in-game with larger mines hoping to gain more spoils from my mines.