I may be very wrong but I suspect that lowering the weight of the wheels will not decrease the weight on the suspension and, thus, would not increase your payload.
Happy Camping! ///// Richard D.
2006 4x4 Ford 250 SD / 2007 Flagstaff 827 FLS
One very patient wife and one furry child who travels with us. Forty-two years of trailering and camping, and I still have a blast.