The larger the crowd, the larger the purse. Some have done well by broadening their audience. There is an enormous market for motivational speakers, especially if you are funny and entertaining. Once you're famous the thing feeds on itself. People will want your books, tapes, videos, notebooks, programs, maybe even your picture.
Fame is profitable.
Seeing this local profit-taking you might be tempted to set up a fixed fee for your services so they don't take all the profit. That sort of fee adds up. Other preachers have made bundles in the past. Consider John Wesley. He was one of the richest preachers of all times.