First of all I love your videos and thanks for the feedback.
Regarding the game speed I had several ideas to improve it from a simple button to multiply the game speed to making the combat phase less passive (Coins that can be collected by clicking, choose temporary power-ups at the end of each wave, or active abilities that can be activated at the right time). Fortunately, the systems are set up in a fairly scalable manner although some code refactoring is definitely needed.