I've been at DLR that weekend each of the last 5 years. The parks are busy but manageable. Most of the major attractions had queues around 45-60 minutes, with only a couple attractions beyond 60 (RSR, Splash, Space/Soarin' at times). But given how they've
Due to the races, the traffic on the surrounding streets will be difficult at times. If you're not within walking distance, don't try to get to the parks before ~10am on Sunday, since road closures will be in effect and thousands of runners will be trying to leave while tens of thousands of day visitors are showing up. That said, if you can get to the parks during that time, they should be deserted, so I highly recommend it! Saturday will also have some road closures early for the 10K, but they should be done before the parks open
If you're expecting it to be busy, you shouldn't have any major problems. Yes, there will be lots of people, but many of the APs are blocked out that weekend so the other guests are mostly out-of-town visitors which makes everything a little more pleasant. Haunted Mansion will be closed to install the Christmas overlay (because that makes sense during the last weekend of summer) and there are the Star Wars-related closures, but practically everything else in both parks should be running, including a full entertainment calendar