My main gripe with most of the FONV DLCs is replayability, or lack thereof. Sure you can always revisit Zion Valley, but unless you are gathering or green gecko hunting, I see very little point to. I barely see any white leg remnants. Do they ever respawn after the quest is over? In my experience at least they don't.
I especially don't like the fact that NONE of the NPCs that you dealt with particularly Graham who served as Zion's only vendor all disappear from Zion, no matter how you choose to resolve the conflict. I have been nice if a even "generic" Dead Horse or Sorrows member took over that "vendor" role, which would have given me a reason to revisit Zion. Or maybe had a chance of saving the Caravan from the beginning and use them as both a vendor and as means to travel to and from Zion.
It would have also been cool IMHO, if you could have asked one or both of the followers to stay in Zion and be your follower while you visit there.
Occasionally I'd revisit Zion for the view and chance of scenery, but since I've been playing Skyrim the need to even do that has been practically eliminated. I actually like the "Randall Clark" side quests better than the main HH quests and I especially enjoyed disarming and using the Survivalist's caves as my "home bases" while in Zion.
I don't really see the point to returning at all.
Once the quests are done then I fail to see why I'd ever want to go back.
Even if Follow's Chalk and Walking Cloud stayed, even if White Legs respawned, even if there was a vendor to take Graham's place, I don't see the point to it.
I mean, unless I go back to find the rest of the entries for that depressing dude the only thing to do is kill stuff.
Same goes for just about every DLC.
Why go back to Adams Airforce Base? To kill stuff and collect unique's you forgot.
Why go back to The Pitt? To collect stuff you forgot and/or kill stuff.
Why go back to Point Lookout? To collect stuff and kill Trogs, I mean Hillfolk.
So replayability with the same character? There is none.
Replayability with a new character? That there is though.
Should there be replayability with the same character beyond killing/collecting stuff? I dunno. Maybe? No idea what that would be though.