I purchased Superior leaf helper springs and installed them today (no rivet used). I am happy to report that there is a noticible increase in stiffness of the ride with these installed. In giving them the "test" I actually did a little "spin out". I am very aware of my tires wear and never purposly spin out, but seems like much of the axle wrap is controlled.
All in all, ride is stiffer, with greater rear-end stability.