Maxed jumbotron (total destruction), took some time to align my aim so that I can hit the ball in a perpendicular manner with the upper wall, spent the rest of the game stationary spamming mouse clicks (carefully bringing my pointer to the same spot after shopping). I don't think any enemy could reach me before I hit 5 times no matter how many they were =) All other upgrades were pretty much just for eye candy.
Anyway, this game is a good example of why I like to come and play games here. This is a very simple and working formula for a casual game. You now have a good skeleton to build something great.