We've been to Disney twice before for the 4th of July - and we'll be back again this year!!! IMO, it really isn't that bad. What we find that works for us is to get to the "early entry" park as early as possible. Of course, use Fastpass!! Around 12:30 or 1:00 pm, hop on the bus back to the hotel and take a nap/swim break. Around 5:00, we go back and stay as late as we want.
On all of our visits during the summer, this worked really well for us! We were able to see everything we wanted - the kids got to ride their favorites many times, and the lines weren't really that long.
We'll be at Epcot this year for 4th of July - and from what I remember from last time, they have a fantastic fireworks show there!
Enjoy!!!