I didn't see a difference in 4th of July crowds myself. But here is the advice I always give: Disney World is the most visited place on earth...there will be crowds. Don't expect low crowds and you'll never be dissapointed...only pleasantly surprised when there are.
We just got home from a 5 day trip and the crowds were at level 8s everyday...I think we were park touring the same as everyone else, because one day I went off by myself toward the end of the evening to MK (wed) and it was empty. Probably a level 5 or 6!! I couldn't believe it! I took full advantage of it and had a great time!