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I would not because it keeps idiots in parking lots from putting dings and dents in your doors. But if you do, you can sell them on the board for a little. Go get you some fishing line and an eraser wheel if you have not already.
They spears do help with people in the parking lots, but it comes down to personal preference. I personally do not like the look of the door spears. They look out of place, unless you color match them to the truck.