Just an update that is hopefully helpful to future visitors, although YMMV.

The rehearsal on July 3rd on the Capitol grounds was well worth it for the portion that I saw. I walked from the L'Enfant Plaza metro station to the west Capitol grounds. If you aren't carrying anything and you don't have your pockets full of stuff, security was very easy (all I had was a water bottle and a McDonald's take out from the L'Enfant Plaza location.) I had planned to just stand, but found a seat on a ventilation grate (no ventilation occurring.) The rehearsal started on time and had a 10-minute intermission at 2045 hours. That turned into about 25 minutes. Once it started again, 3 acts had to re-rehearse (not sure what the issue was as all 3 sounded great). After that, I saw significant lighting off to the west and didn't want to get caught in the storm. Perfect timing because about 5 minutes after arriving at the hotel in Crystal City, the skies opened up.

I also spent some time on the Mall on the 4th. While I had no plans to attend the fireworks on the Mall, I did enter the secure area midday, at a designated entrance point, to walkaround the Washington Monument over to the WWII Memorial. I've heard stories about how long the security lines are for this event. Maybe, maybe not. Security was again easy (in fact easier than the Capitol as there were not any metal detectors). Again, if you aren't carrying bags, coolers, you are waived through.

I stuck with my Gravelly Point plan. An easy (15 minute) walk from the Crystal City Crowne Plaza on the Mt. Vernon Trail, with a chair, a water bottle, and a slice of pizza from Amazon Fresh (a block from the hotel). I setup my chair where there was the biggest mass of people figuring that many of those people have done this before. Maybe, maybe not. This group had a view of the Washington Monument and the Jefferson Memorial. When the fireworks started, it was hard to see the full effect, and EVERYBODY picked up camp and moved closer to GW Parkway. Not sure if the firing location had shifted from past events or the vast majority of the people were also new to this.

A couple of comments. Parking was available at DCA and there is a walking path that connects to the Mt. Vernon Trail. But it appears that northbound GW Parkway was closed after the event to allow pedestrians to leave Gravelly Point. Many cars were parked at Gravelly Point and along the grass areas on the NB side of GW Parkway. Those cars weren't going anywhere until the pedestrian traffic thinned out. Also, bicyclists were a problem. The trail is very narrow and even with all of the pedestrians, bicyclists were trying to do their thing, but acting like toddlers when toddlers got in their way.

There were lots of fireworks to be seen from the area in Montgomery and Prince George's Counties. Also, does DCA do a ground stop for the fireworks? As far as I could tell there were no approaches or departures for about 30 minutes.

If I do this again, I noticed while driving home along NB GW Parkway yesterday, that if I walked another 10 minutes north on the trail, I would have had an even better view of the fireworks. FYI...

I may go back and edit this post to include some pics, but can't get to it today.