I've watched and played most of it including demos (skipped/didn't play Comrades, King's Tale, Monsters of the Deep, or the mobile games). First time around I had only played vanilla XV a couple months after launch (before the big chapter 13 update) and had watched the movie and anime. Sometime during the past year, though, after all the DLC was finally out and finished, I replayed it in its entirety.
As someone who enjoyed the gameplay and character banter but thought the story was a huge disappointment my first time around, there is some improvement with the inclusion of the DLC and patches/updates. Mostly it improved the bros' stories (well, Ignis and Prompto's, at least), and provided more context for the plot and background lore. It makes the game feel a bit more solid, especially if you play the DLC during their relevant points in the game, and it did better my overall experience with it. However, the story problems are still there; the DLC is really only a bandaid at best. Luna still gets jack all screen time or importance, second half still feels rushed, story still feels cobbled together, etc. If XV had redeeming qualities for you when you first played it, I think experiencing it again with all the DLC and side content included is worth it (and again, especially if you play the DLC as they happen in the story), but if you really didn't like the game in any way to begin with, don't bother. The DLC and updates/changes won't make the difference.
Personally, I'm glad I replayed it with all the extra content, though, even if I'm still overall mostly disappointed with the series. So take that as you will, I guess, lol.