How about increasing the obstacle's health each time it is destroyed to encourage destroying other than just one obstacle FOREVER. And/or each successive obstacle yields an increased in $/HP. It would reward advancement up the chain. As it sits now there is no difference between hammering the Devil in one shot versus the Moon
 "The Perfect Tower"){kind=icon}
 "Learn to Fly Idle"){kind=icon}
 "Paladog"){kind=icon}
I like that idea!