Everything except for the endings can be seen by just playing through the game normally regardless of how well you're doing. The boosters are meant to make the game experience easier for players who are struggling. If you've finished a playthrough, you very probably have enough points to get at least one booster even if you've lost. I think that the difficulty level in the finished game is fairly reasonable and has plenty of ways to be adjusted up or down, but I understand that the core gameplay isn't for everyone.