This is cool. After about 20000 points only the green ships appear, and it becomes extremely easy.
I think you should have an alternate control scheme where, when the fire button is depressed, you have autofire, and when it is not depressed, you automatically charge the super-weapon. This would offer virtually the same functionality as your current scheme, since there (as far as i can tell) is no penalty for charging your weapon and keeping it charged for any amount of time. You would still be able to tap fire to shoot in a more measured way in this mode, provided the time between shots in autofire is greater than the time it takes to tap the key.
You'll be able to click on this someday.