The 3M double sided tape is designed to hold trim pieces down on automotive applications. You can glue a piece (properly, 3M surface prep, etc) and then proceed to hang from the piece with all of your body weight and it wont come off.... Any other method of attachment would require the drilling of the spoiler, which would not be easily repairable after the fact. Plus I'm sure you are aware of how hard it is to get oem parts...

I held the gauge pods down on the dash of my 240 with the grey 3M tape, its so strong it pulled the material off of the dash frame

Its also used on our Z06 to hold the carbon fiber trim pieces on the car (rear wing, rear carbon lower valance, carbon fiber rocker panels)... 220+mph and they stay attached.

The 3M tape is a lot stronger than you think, when properly applied