I think there should be some sort of reward for getting more stars on levels. You've mentioned time and time again that the upgrades are meant to be passive, but maybe you can spend stars on permanent upgrades or something
Tips for getting the Hard badge:
1. Start off with a good amount of money in the bank. Maybe about $5000
2. Use whoever except for Barry Zooka, you aren't going to be doing much putting.
3. Buy these three powerups for each hole: Airboost, Super Stop, Powerswing. Super Stop is easily the most important, so you can stop the ball at the right time so it'll land in the whole without having to putt for an extra stroke.
4. Your goal for each hole is to get an Eagle (2 under par) or better. Use your Airboost and Powerswing on your first shot, and on your Super Stop on the final shot to get it in the hole.
5. If you can't get it, quit and start the hole over. Do this until you get a satisfactory time, and then move on to the next hole.
6. Pay attention to the wind, it can make a big difference.
7. Stony Beach is a lot more difficult to conquer that Sunny Andrews. Keep at it. I managed to get Stony Beach in 342 and Sunny Andrews in 334.
Best of luck