A little bit of clarification.
If you have adhesive residue I'd use an eraser wheel + drill on it, which is what most guys will use.
Once that's done you can wipe it off with some bug/tar remover, I use PPG 330, but you can use whatever you like.
I would then use wet-sanding to remove any imperfections, and I'd start with 2400, maybe have to move down to 2000, then go up with it until it was super smooth before buffing.
This guy buffs with power, but you can do it by hand, no problem at all. Watch this video and you'll be an expert, it's so easy.
This can be done in 15 minutes tops if you know what you're doing, but if you don't it could take a bit longer.
The only thing is, most guys don't have several grits of sandpaper, PPG 330, buffing pads and compound laying around, so no worries if you want to take it to a body shop, it'll be quick work for the, but CERTAINLY doesn't need anything repainted/resprayed, just an adhesive removal, clean, sand, buff, and it's ready for the new spoiler or none at all.