I think I have played about 18 scenarios now, around 13-14 are done and we still only have 2 or 3 prosperity checkmarks.
Any suggestions on pushing Prosperity?
Go back through your completed scenarios and make sure you actually applied all of the prosperity you earned. We noticed we had forgotten to check a few ourselves. Also, you could consider looking into the spoiler tag below if you really want.
Spoiler (click to reveal)
Donate to the church. After cumulatively donating 100 you gain 1 prosperity and than another 1 for every 50g donated thereafter.