If you play through Stage 1, choose your upgrades, continue, and then quit game at the beginning of Stage 2, you can then press 'Start', load your game content, and start a 'New Game' at what ever difficulty you wish, and once the new game starts you'll still have the upgrades you had previously at the beginning of Stage 2! Repeat this process as many times as you like. You can do this same process between any 2 stages, so if you get bored of playing through one stage, you don't have to keep playin that stage to do this.
Easy + Overall 'S' Result = 180 pts
Normal + same result = 250 pts
Hard + same result = 350 pts
