no spoiler on the Sky for me, thank you.
I think the look of the rear looks cleaner & less busy without the spoiler to disrupt it's smooth lines.
If you want the spoiler purely for cosmetic/appearance reasons then I say go for it.
I'm sure the aftermarket will make some different looking spoiler besides the one offered by the factory if you prefer that. (just hope I don't see a Sky on the streets with one of them huge aluminum shopping cart wings one day, lol)
For all practical purposes though, a spoiler won't come in handy unless you're frequently going over 100 mph. That's when the extra downforce created by the spoiler will come into play.
At slower speeds it can actually create extra drag of the airflow around the vehicle.
So it's all a matter of taste, go with what you like...either with or without "wings", you'll still be flying high in the Sky.
