Just a few suggestions: Make it possible to kick someone out of the kingdom, like the girl who eats too many sweets.
Also if you can make the change that happens to the monster treasure chest permanent.
Perhaps set an in-game time limit. Like you have to have "X" gold and people by "X" many days.
Another idea could be that after you've made alliances with other neighboring kingdoms you can borrow money from them if you go into negative. They the king would send someone to you to collect once you have double the amount you borrowed.
Thanks