Are you talking about the piece over the back window? If so, I wouldn't know but I don't think it would look to well on the MSP. Although it would be nice to see how it would look.
^ They do and it doesn't look half bad. It's alot more subtle than the STi one and will need to be painted unless you're a fan of it's rubbery black finish, or so I've heard....
Actually this, or vortice generators would be a good aerodynamic addition to our car. Anyone who has seen the way snow or water get blown off the back, you'll notice that there's a delamination of airflow over the center of the back window and a low-pressure zone at the bottom of that dead area.
Adding aerodynamic devices to the top of the car would either get rid of that low pressure zone, decreasing drag and increasing fuel mileage, or increase the amount of air hitting the rear wing, increasing high-speed downforce/parasitic drag.
1) Because its fun to make you look stupid
2) Easy to do...
But Vortice generator is the more correct term because that's what it actually creates. Its an aviation term, and as a pilot, hard to break the habit...