Once you’ve figured out a play level and play style, you don’t need more than a small regular supply for lives, missiles/mines etc, and fuel. I never spend keys now because I have all the shields, starting power levels, and travel speed boosters I need for playing regular missions without any difficulty adjusters, special weapons etc
Can you be more specific about the “issue” you are trying to say here? Judging by the topic’s name, Keys is the most important element in this game since it gets you completed with everything you want.