If you're not doing any heavy duty hauling, you're probably alright with the set-up you have currently. The airbags are pretty much a supplemental aid if you do plan on hauling a load, and/ or towing a trailer.
I would suppose the A-body springs are stiffer than the stock wagon springs. I have cargo coils in mine. The car sits alittle too high for my liking. However, I've towed vehicles and had the rear loaded down with several hundred pounds of body panels (5-doors, tailgate, bumpers, fenders, etc.
I would consider going with the A-body springs...maybe adding the air bags later.