Air bags help support the load. They keep the back of the truck from squatting so much. If you're not over your weights I doubt they will do much for you other than raise the back end a bit. I don't think a smoother ride will result. There might be some improvement if your current suspension is bottoming out on bumps.
If you completely removed the rear springs and went with a complete air bag only suspension then you probably would get a smoother ride. However, this is very expensive and I'm not sure it's even available for a 1500 truck.