I did post on the other thread about our experience last year with the parks on July 4. Basically we found the parks to be busy but very manageable that day. We had been worried about parks reaching capacity etc etc, but that did not prove to be the case. However we did make some advance bookings to get the most out of the time there. We arrived on Sunday 3 July, and used the Aladdin's parade dinner package (3.30 pickup) to see the first show followed by fireworks . Looking back at my bookings we also had a table at Tortilla Joe's at 7pm. My plan was to use that if the parks didn't seem full. We did go out to eat there, and came back in to our parade spot with no difficulty.
On 4 July we had prebooked WOC dessert party seats. Again we intended to park hop but pay attention to the crowds and move if we thought we were in danger of a park closure. But again, there was no problem. DCA was very quiet. Walked on to TOT - obviously that will have changed now

Stopped into Carthay circle for a drink - tables no problem. (Downtown Disney was very busy though). There was nothing particularly special about 4 July in DCA that I recall. However there wasn't that much to notice at DL either. We are not from the US and had expected more actually !
My guess is that APs have a huge impact on these dates, and as others have found, it's sometimes busier on the days leading up to a blockout than on key holidays themselves. Certainly we had found a pre xmas visit (early December ) felt busier. As the OP suggested there have been plenty of changes over the last year. But I think with a plan, an early start and a few strategic bookings, you'll have a great time! If you are going to be in DL for July 4, I'd go for a dining package, so you wil see the fireworks with ease.