My overall philosophy is this:
"radical" visual cues should be the last thing done to a car, not the first. (Be fast, then look fast).
A rear spoiler such as that looks hot on a real race car because it's part of an overall system designed to improve the car's performance at very high speeds. This system includes some kind of downforce generator at the front (either a splitter or some kind of "tunnel" venturi), not to mention a radically--and unstreetable--lowered suspension.
As it stands, that spoiler looks completely out of place, decreases your top speed, and actually could reduce your stability at high speeds by changing the front/rear lift ratio to a more rearward bias. That is, your front end may feel "twitchy."
