It's not going to affect it much (plus, it strains the remaining leaves right at the axle mount). The factory overload's primary function is to stiffen the suspension as it squats down from having a load in the bed. Without a load, there likely isn't much contact between the bottom of the spring pack and the OL leaf.
Some better shocks (and poly suspension bushings) may help, although washboard stuff is pretty nasty no matter what you have.