Well I think the main difference of course will be the set list. Usually with U2 when they play multiple consecutive shows in one city, it's usually almost the same setlist with a few modifications here and there. But from Bono's recent quote on the new tour, sounds like it's going to be much more varied between consecutive shows.
Usually in these cases, I just see one of the shows. But due to the circumstances, I think I'll be buying a ticket for both nights. Hope the difference is significant!