The last two parks on the race circuit are DHS and then EPCOT - around the World Showcase, MK is about the 1/2 way point and most runners are out of there pretty early.. It is not a big hassle to have the runners going through the parks and the course is clearly marked off. Please, do yourself and the runners a favor, wait for the CM's to tell you to cross, don't cut off a runner. Speaking from experience, when going around the World Showcase (anticlockwise) the runners are 25 miles into the race. My physical reflexes are not what they normally are at this point and I am running on total autopilot. If you try to zip in front of me, I will not be able to avoid you, and we will crash.
Other than that, the parks seem pretty much normal. As was said, there are some road closures, but other than that, no real impact to crowd levels..