A spoiler of the sort that is normally put on a 4-door sedan is of little or no functional use. There is no danger that the rear end will leave the road at any speed you are likely to drive the car. On some cars, like the Infiniti J30 and the early 90's Nissan Maxima, they serve to uglify the car considerably, in my opinion. Of course, they are far less functional on a front wheel drive car.

I tend to think of a spoiler as a tattoo: unnecessary and expensive, but a matter of personal taste.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)