I see sites like Arnott offering Air Springs 2006 Buick Lucerne Rear Air Spring Pair at 1A Auto.com.
Do they replace the coil springs or the air shocks or both? How do they ride?
Or are they just the old helper spring thing?

if you go on the gm parts diagrams it just looks like all the bonnies and that, which is a coil spring(on the control arm) that is mildly assisted by a air shock. the load leveling inflates the air shocks to level it with a load. i dont see alot of gain from swapping this stuff on to a vehicle that didnt come with it unless you carry a full load of people and a trunk full like 80% of the time