I am by no far a Dcity expert. I just bought some cards a couple of times and then abandoned my city to its own fate. My citizens can do all they want for all I care, as long as they give me their fair share of SIM and I dump it for hive.
Now, back on topic. @bala41288 informed me a few days ago that he has created this awesome tool that tells your right away how much money (in hive) you have put in and how much you have received:
In just 4 months, and despite not being active at all, I have made about half of my initial "investment" back! So, in about 4 months more I will have made everything back, and that without selling a single one of my cards! Very nice!
How is your city doing? Go check https://dcitystats.com/ and leave me a screenshot on the comments!