The marathon does not really increase the crowds in the parks much, you will find that there will be light crowds pretty much any time you go after kids go back to school. With the 5K being the 9th this year you will see more runners coming to the resorts starting the 8th and increasing each day up until Saturday. Saturday and Sunday you will see more runners in the parks with Sunday the most busy but it will still be pretty quiet with lines being very manageable. After Monday most will head home and the parks will pretty much empty out. The biggest impact is traffic each morning during the races and dining reservations are tough to get, especially Friday and Saturday nights.