Why bother: coin boosters cost 300 energy for 1 day. This can give you up to 30 extra coins a day (based on 30 games a day, my personal absolute max before my brain explodes). This can be used to get 3 enamorocks. If sold on AH, enamorocks can get you around 850+ crowns each, or 10+ energy. To sum it up, if you're going to use extra coins to get crowns, you'll get 10 times less than you'll pay.
Suggestions on balancing Coin Booster price/performance ratio without breaking existing system:
1. Lower Krogmo Coin Booster price.
They're a little hard on the wallet at 300 energy each. Make them 50 energy, not good enough to be profitable, but cheap enough to buy a couple.
2. Increase amount of coins given. Give 3-5 extra coins, for example, but limit to 1-3 coin boosters at the same time. Keep the 300 E price.
3. Make them last!!! 1 day isn't nearly enough to make any use of it. Possible variants include 1 week long coin booster and 1 month long coin booster. 1 week would be priced at 300 energy, 1 month - 1.000 energy.
Mix 2 and 3 and you'll have a much more attractive package. I'll certainly buy one. Or few.
You can only play 30 games a day? Heh. I guess you haven't undergone the human-to-computer integration yet.