It won't have much affect on your trip,probably the biggest thing is that Epcot might close at 9pm on Saturday which is the time it closes most of the year instead of 10pm which is the time it usually closes on Friday and Saturday during Food and Wine.This race starts outside Wide World of Sports at 10pm then heads to an already closed AK and DHS before reaching Epcot,the fastest runners might start reaching Epcot at 11:15 with the last ones reaching Epcot at close to 2am.Epcot will be open at 10pm for runners friends and families with tickets to the after race party that goes till like 3-4am.There is a short 5K race early in the day that also shouldn't have any impact on park goers.I believe in 2014 the race was held the final week of the festival so crowds would be huge because of that but I hear in 2015 the festival is extended an extra week after the race so it should ease the crowds a bit,basically the only affect would be seeing buses to the expo from the resorts and runners wearing medals on Sunday.This race also has fewer runners than the main marathon weekend held this past weekend which had over 80,000 runners between the 5K,10K,half marathon and full marathon.I believe Wine and Dine has like 14,000 runners for the half and probably a couple thousand for the 5K,definitely fewer people.
