Thank you for the great feedback! I really need to prioritize the development of an in-game explanation for the currency system, so I appreciate you reminding me of that concern. When you complete a level for the first time, your score is added to the amount of money you have in the game, but if you replay a completed level, the amount of money you earn should be the difference between your new high score and previous high score. It's a bit unintuitive, but it's meant to incentivize seeking a higher score. As a solo-dev, I don't want to overpromise, especially when it comes to the timeline, but I intend to polish this demo before continuing the development of the full game, and I hope that at least some of your concerns will be addressed with future updates.
Thank you again for taking the time to play my game and provide feedback! I'm glad it was fun!