We presently have and have had several 5th wheels, but the principle is the same as far as what you are asking. With extra leaf spring(s), your tow vehicle will always ride higher and have a stiffer ride. If you use air bags, you can adjust the pressure to the height and ride to what you want, when towing or when you not. You will not be high or stiff when not towing, to us that makes a big difference, as all we have used are dually's, which are stiff to start with. LOL. On all the trucks we have had, I installed Firestone's Ride-Rite, with in-cab gauge and the ability to change the pressure on the go, but there are other brands. I would say check the air bags out, pricing would be about the same, when you look at what you gain.
Hope this helps and God bless,
Mike