Science, and especially medicine, hits a wall periodically. In a period of about 50 years, with the help of two wars, we went from fabric covered wooden fighter planes, powered by reciprocating engines and pulled through the air by propellers flying at 120 MPH, to all metal jets, capable of speeds exceeding Mach 2. Some 55 years later, there still aren't too many fighter planes much faster than Mach 2 to Mach 2.5.
Much like the science behind aircraft, the science of medicine made leaps and bounds in the first half of the last century. And it has actually kept pace with the the science behind aircraft.
As you pursue any technical goal, the results you achieve in exchange for your efforts rapidly each the point of diminishing returns. The gains are fairly big, at first, and get ever smaller for every period of time you spend.
In addressing the original subject of Jerry Lewis and the MDA, a massive amount of money is spent on improving the lives of those suffering the various diseases that fall under the MD umbrella. For example, when I was building custom vans for the handicapped, I saw what went into a van for a young boy suffering Duchennes MD. The van for that boy rapidly approached $60K. His wheelchair was over $10K. These children (all three boys in his family were afflicted with Duchennes) rarely live past 25. They know about the missing gene in children with Duchennes, but they've not yet been able to splice the gene into these children.
Having been personally involved with some of the things the MDA does, and having seen Jerry Lewis personally attend to the needs of a child and his family fighting (and often losing to) this disease, I have no question in my mind as to their dedication to finding treatments and cures for the diseases they research. Before you question their sincerity and their veracity, try devoting some of your time, and see what really goes on.