Ignore Quickpaw. Dilts36 advice works fine. I bought the shield after the first boss, the heat seek after the second, the was able to get all the regular upgrades and beat the game.Ignore Quickpaw. Dilts36 advice works fine. I bought the shield after the first boss, the heat seek after the second (it's great for the bosses), the Inferno and EMP after third and the exploder after the fourth. All the other bonus points I spent on the interest and I was able to get all the regular upgrades and beat the game. Just be sure to spend as little as possible until the level before the boss.
It's long, but it saves your progress automatically so you can just play a little, and then come back when you want.
A pity you can't edit your profile though!
 "Battle Pool"){kind=icon}
 "Shield Defense"){kind=icon}
 "Jigsaw CHATTINNG 2.0"){kind=icon}
 "Bowmaster Prelude"){kind=icon}