The reason why I made it so you always get 5 coins back after buying syrup is so you dont end up with nothing and having to go back to the first car to get more money. Also, the tip system was to give players a sense of a final score while making sure they still played the game instead of holding onto a ton of coins they earned in earlier rounds.
I do agree on the music aspect. I plan on adding some original songs soon. I've also made a patch that fixes the issue with the Bronk'r game.
Thank you for your feedback, having nobody else to give insight on the balance of your game while developing it makes it hard to get right.