This isn't a suggestion for gameplay, but instead an idea to help the game financially. I think it would be a really good idea to have special sales for coins.
For Example:
Spend 2.99 for 5% more coins, 5.99 for 10% more coins, 10.99 for 15% more coins, 20.99 for 20% more coins, 54.99 for 25% more coins, 104.90 for 50% more coins. This is just an example of what I mean.
If you give temporary weekend, weekly or holiday specials on coin sales then this could benefit not only the player for having more coins to expend, but for the game devs out themselves for making better profits.
I'm currently employed as a Produce Clerk/Meat Porter and every time the Produce and Meat Departments have a weekly specials on a certain item such as apples, grapes, bananas or pork, chopped meat, and boneless pork loins the sales on those items during that week spike up tremendously. Our Produce Department has been commended last week for having the highest sales this year out of all of the Produce Departments in the entire company and the weekly specials we do have a great impact on it and helpes us a lot.
So, with that being said. Having a special on coins every now and then wouldn't hurt and could definitely help the game dev out in finances in turn. Pay to play so to speak. I've learned appreciation can go a long way.