They absolutely aren't worth it in the sense of value-add if your only metric is performance, they cost far more than a traditional quality spring set up, especially with labor, for marginal (if any gains).

However, in the realm of "money doesn't matter," you can get quality air suspension systems that are comparable and (arguably) superior to other systems without substantial weight gains.

Most of the people arguing "but you can do air bags right" are technically correct, and there's just as many people abusing a "traditional" set up (slamm'd and stanced or whatever),and probably far more so, than people that are custom modding air rides to their cars.

Still, I personally dislike the look. And my only problem with it is the greater crap that enters the used market from the "more money than sense" people that aren't trying to "do it right" but just achieve "close enough to look legit," and their far from limited to ruining their cars with just airbags.

tl;dr Air bags are fine when done right and taken care of. They are not for performance on a budget, and don't necessarily add a huge amount of weight depending on the system, and if you're willing to throw the money at it, air suspensions can be just as competitive on the track.