I love dCity. I accidentally got into it at just the right time and have a fair amount of cards without much investment. So far, 99% of the cards I've bought with SIM have just been the random selection from the purchase tab.
I really want to try to figure out how to maximize my SIM return. I don't know if I need to get rid of some cards or what. It seems like every time I buy new cards my SIM income barely adjusts; sometimes it decreases. So I gotta figure out the best way to do it!