In my area, considered one of said affluent areas, I know for a fact that most of the elders are giving the CO cash every time he comes. When I was still mentally in I was regularly giving him $50-100 depending on how I was treated during the visit.
We had 11 elders at the time and some were financially more well off than I was so average lets say each gave $50 so thats $550 just from the elder body, from 1 congregation in a 12-20 cong. circuit. So I think yes they clean up in some areas for sure.
Keep in mind that this was a estimate based on elders giving only, its all tax free (unreported) and they have a free car, free gas, free dry cleaning, free place to stay, free medical, free dental and in many cases free food.
Do the math. These guys are doing ok I think.