From a fellow passholder, I'd say it's definitely worth it, but I love Fourth of July at WDW (leaving Wednesday for my fifth Fourth of July trip to WDW in a row). Yes, it's insanely crowded, but in my experience, it still is less crowded than Xmas/NYE (done that at WDW as well). This summer is also looking less crowded with the South American economic downturn and Brexit cutting into international crowds. That said, MK will still probably close to capacity in the early afternoon, though I've never seen it get to a level where Passholders aren't permitted entry, so you shouldn't have to worry about that. If your priority is just the fireworks at MK (which are AMAZING!) and not necessarily attractions, I'd drive up in the morning (aiming to get there before noonish just to be safe with capacity closures and stuff), have your three FP+ selections for early afternoon, and make an in-park ADR that allows you at least 60-90 minutes of time before the fireworks to stake out a great spot on Main Street.
You mentioned trying to get a table at California Grill. The view, while not as great as Main Street, is still very impressive, and I was really pleased by my last meal there in March. While getting an ADR for two within a week will be difficult, I believe I was actually able to do it for the day before the Fourth (which they also show the fireworks on) a few years ago. You might try also for Narcoosee's (which is where you'll find me this year). One tool I recommend is the new Touring Plans Reservation Finder. You do need to create an account with TP but do not need to subscribe, so it's free. This is because it's still in Beta testing. Keep in mind, it will just notify you (I would recommend turning on text message alerts) when a reservation becomes available, so it remains your responsibility to actually log on and reserve it. It will search for an hour before and after your designated time. So I'd put it 7:30 or 7 given that the fireworks are at 9. Here's the link:
https://touringplans.com/walt-disney-world/reservation-finder
Also, Epcot hosts a wonderful 5 or so minute long Fourth of July fireworks tag to IllumiNations that is impressive as well.