Definitely not the case. I have played through all the Kingdom Rush games, fully and doing all the bonus objectives, without spending a dime beyond the initial

Definitely not the case. I have played through all the Kingdom Rush games, fully and doing all the bonus objectives, without spending a dime beyond the initial purchase. I had a great time too, and I have a pretty low tolerance for grind. I think the KR games are exceptionally well designed in this regard.