Nullus, agreed. I forgot to mention how I handle event sheets. I create a single, all-encompassing event sheet that contains basically anything that's likely to happen more than once across my levels. This includes player controls, UI, enemy interactions and debugging.
I then create an event sheet per level to handle that particular level's parameters (enemy spawn rate, enemy types, total number of waves, etc.) which are passed on to the main event sheet. Each level event sheet includes the main event sheet.
I also put all my global variable in their own event sheet, just to keep things neat.