Well, hey! Feedback is what makes a game grow. You cannot know everything people think of without feedback. You have excellent graphics and a lot of possibilities. And since your game is simple, exactly how I love them, it's worth to see possible updates. Your ideas are good too, did not think of these. If you keep it out of the pay-to-win or online-competition scopes, it's perfect for me. The only thing that should be kept saved is your highest score to know how to surpass yourself.
AND, I can add this, money-wise, if you want to keep the game simple, there is a money gaining with watch-to-gain methods. Basically, a button on every start of game that permits you to see an ad to gain special abilities. So anyone can simply NOT click the button, therefore, no ads, never. Its a way to gain little money without harrassing anyone because absolutely no ads are forced and the game is perfectly playable without ads.
Now, that being said, once you get some powerups to happen, you can start thinking of a soma-coin mechanism to permit you to have x-seconds of a particular boost to begin with. And of course, nothing online, just local stuff. Your game has so much different possibilities and THAT without any ads or harrassing stuff.
These are just ideas I throw, but you are the author and I think, with your graphics and ambiance, your game can become popular easily. Keep it up and you don't need to do big upgrades, you can do small upgrades on a weekly or bi-weekly basis without stressing out with huge versions. People like me will simply enjoy short games like yours without the ad-hassles and making it calm and smooth.
But Good Job again for the idea and simplicity, continue!!!