Cosmetic and NVH, no measurable gain on a track. They put them on Buicks for the same reasons. The body of your car isn't exactly flimsy, this isn't a fox body.
The motor is the last thing I'd be worried about breaking. It will handle it.
Halfshafts
Transmission
That's where my guess would be for the first things to let go.
They'll do the Whipple one it's the exact same thing.
The stage 2 has a much better tune, smaller pulley, bigger throttle body
You could call whipple and ask if you can just add it after the fact
https://whipplesuperchargers.com/i-2678-s650-mustang-stage1-stage-2-upgrade-kit.html
The media said:
Ford reports that the addition to the spoiler is effective at speeds as low as 30 mph and encourages drivers to experiment at the track with and without the Gurney flap installed.