I was there a couple of years ago during a the parade taping. Other than the fact that Main Street and the hub in front of the castle were congested that day, I didn't pay all that much attention. It didn't seem to have much of an impact on crowds.
That was on my one and only solo trip to DLR because I was in Anaheim for a conference. My biggest worry was that I would end up on camera and my daughters would find out I had gone to Disneyland without them. My DH and I used the euphemism "trip to Anaheim" since they were too young to know just what that meant. (That wouldn't work so well these days now that they are 9 and almost 13!).
Anyway, bottom line, I didn't notice the parade itself having much of an impact on crowds other than some congestion on Main Street and the hub.
I'm so excited to see the parade taping! I watch the parade every year and have since i was small, and it's been a dream of mine to see it live! This doesn't even seem real to have one trip coincidentally at the time in Disney World and to have the option to plan a trip to Disneyland.