The wheels are part of the unsprung weight, so reducing weight there has more practical effect on ride and handling than on CCC. Technically, though, with lighter wheels you would still be reducing the unladen weight of the coach and thus giving more CCC, on paper anyway.
The question is, are the wheels actually enough lighter to justify changing them? That will depend on what you now have and what you might buy. Aluminum isn't always a lot lighter than an equivalent steel wheel and new high strength steel alloys can be very, very close to aluminum, especially in smaller wheels (15-16" sizes). But odds are your existing 19.5's aren't made of ultra light weight steel alloys either.
The folks hawking aluminum wheels say they can be up to 35 lbs lighter (each) than steel. That's for a 22.5 x 8.25 wheel, just about the largest.
Looking at some sample wheel weights for a Dodge 19.5" rim, I see steel wheels ranging from 45-60 lbs depending on size and style, while aluminum wheels are all right around 30 lbs. That suggests you might save 15-30 lbs each if you swap. A total of 90 to 180 lbs reduction in unladen vehicle weight.
As I said initially, the wheels are unsprung weight, so reducing their weight takes no load off the suspension, nor does it reduce body roll.
