@jonathonyule : This is great. Be sure to make it a feature to be unlocked, when the player is doing really great at destroyign baddies, not something you can get by default.
I also just think (IMHO) the score should just not blink and vanish that quickly. Instead maybe they can pop, and fade away... And also, you can add some juice to the scores The bigger the baddie, the higher the font to display the score. And also, change the colors. Maybe gren for normal points, and red for higher points when you destroy the awesome baddies.
Aaaaand...can you implement some à la "Max Payne" mode ? I'd love that.

Holding down RMB would slow down the baddies and their bullets for a limited time, while not affecting the player.
And leave him full space to clear'em all...
Should be possible by hacking the time increment of your game, multiplying dt with a varying factor.