It depends what your tolerance for crowds, heat and the possibility of getting soaked is.
We did it last year, and I will never do it again.
MK closed to capacity on the 4th, and apparently this is not unusual for that date. I am going to guess that is ~75-100,000 people?
DH has now a new level of crowded he calls "MK crowded on the 4th", never seen so many people in one place at the same time. I knew it was going to be crowded, but I never imagined what "MK crowded on the 4th" looked like. Did I mention it was hot as hell?
We thought we will do a short day, arrive in the afternoon, take it easy by not planning on doing many rides because the lines were going to be crazy (they were) and see the fireworks. At 7 pm the park was so crowded it was hard to walk. Main street was elbow to elbow all the way through. It started to pour rain (again common in Orlando in the summer), it was so crowded it took us forever to make it inside a store, even with ponchos we got soaked. After that, DH HAD TO GET OUT, we never saw the fireworks. DH declared he hated WDW.
I am trying to redeem myself with a trip at the end of April next year in which I promised there will be less people than on the 4th of July. Glad he has agreed to go after that because I loove WDW.
My advise will be : DON'T DO IT