Custom rear spoiler for the Missile

from the angles I can see.. It doesn't look like you will get much aero benefit at all unless you seal the bottom or change the angle so it just tips the back and makes a spoiler rather than a wing out of it. Or, you could make it stand up slightly more, and use it as an airbrake, Mercedes Slr Mclaren uses one, so does the Bugatti. See:

[ame="http://www.youtube.com/watch?v=myovuS2vihM"]YouTube - bugatti veyron air brake[/ame]

[ame="http://www.youtube.com/watch?v=mvfG_jEXosw"]YouTube - 2010 Mustang functional rear air brake spoiler by Classic Design Concepts[/ame]

[ame="http://www.youtube.com/watch?v=u7Vb2sIzR9I"]YouTube - SLR Air Brake[/ame]

And a brake pressure switch would be a whole lot simpler than a speed switch. though I would do am manual override switch so you could turn it on or off. It would then be actually helping something rather than just for looks.