Do they significantly vary the show? If they do, does it feel like paying twice for one show with an intermission?
Not very much! I would probably not suggest that someone else does same thing. But usually they adjust the sound a bit and the crowd is less serious for the late show. Once I also had Ralf telling a joke (in German!). The first time I had to wait 3 hours anyway for my train, and the 2nd time it was two special full album performances. This time, well I don't know, I'm just curious how it goes...
I was at few shows, Low for instance, where the late set was pretty much a 2nd set with the same crowd, but not this one!