I'd say that air suspension, when set up well, does not make the ride any worse than with coilovers, but that's another topic. I would buy a bolt on kit if I didn't already have bags on my car. It took me many months and a lot wasted parts/purchases to come up with a decent set. I used Airlift Performance struts for Subaru WRX at rear and Airrex struts for BMW e60 at front. Installing them was a lot like installing BC racing coilovers, so it required welding on threaded collars. Except at rear I needed to remove the old strut tube and make the hole bigger so I could insert the new tube to the upright.
The idea was to get the car high enough to even get out from my garage, which was pain with static height. I think my car looks stupid when all down but I just love the way it rides at ride height. It's stiff, but more progressive than with coilovers. I used to have 250/255 lbs springs and it feels that with bags it grips better on acceleration. I'm running 540 whp, and no issues on street or track.