Do spoilers actually do anything for regular cars on the street, or are they just for looks?

Most of this is in response to Bob Blaylock, who has a misguiding answer.Your stated function is not correct. The function is not to give the drive wheels more traction! Spoilers provide aerodynamic stability. For example, by having some downforce on the rear end, you increase braking stability, as the car wouldn't tip forward as much, helping to keep the rear end planted.You extremely exaggerate "simple, obvious facts". The facts that you present are anything but obvious.1) The front-wheel drive argument is wrong. You don't want the downforce at the front wheels. At highway speeds, most street cars can't exceed tire traction limits by accelerating or slowing down. So it's pointless to add downforce over the drive wheels to aid traction. Instead, downforce stabilizes the car: it reduces the wavering of the suspension and helps keep the car planted. Furthermore, if you did add more downforce to the front, you would further unload the rear end of the car. Given that most front-wheel drive street cars are heavily weight-biased to the front, shifting that weight further forward will make the rear end more likely to loose traction and cause a spin.2) I have sat on car spoilers, and while I am not proud of the fact, they have sustained collective weights of our friends in the high 300 lbs range just fine. Also consider that the downforce builds gradually. The trunk lid is actually pretty strong, and mount points for spoilers distribute weight appropriately. So it's OK and the trunk lids don't crumble: that's why you see touring cars (e.g. SCCA World Challenge) running with monstrous-looking wings that are screwed on to an otherwise stock trunk.3) You fail to quantify what "significant" is for the downforce. 5% can be significant if it means that the balance of the car is shifted that much to the back. I don't have numbers on what is significant.Now, the real argument is that most OEM spoilers are for looks and not performance. This is because of their shape: they are not angled appropriately and not positioned to create a surface for downforce. There's a reason why racing spoilers sit higher on the trunk and have adjustables angles.So while you may get some improvements on the highway from a large spoiler (usually not OEM) it won't make a difference around town, and so you should save yourself the trouble.