As a guy who's now done the 7+ hour WM live and the two nights, both have their + and -
With one night, it made the weekend as a whole easier to handle if that makes sense. On the WWE's old schedule, the one night WM allowed for the HOF Friday, NXT Saturday, WM Sunday, RAW Monday, and SD Tuesday. It was perfect scheduling wise. But the 7 hour show can be draining (WM30 the seven hours flew by because of how great it was but WM34 dragged)
The two night WM allowed the moments for me this weekend to breathe more but I will still a bit tired Sunday night halfway through the show. And the schedule is all jammed up. If you wanna do everything you have SD and the HOF on top of each other, then NXT the next morning, then you gotta beeline to WM, then do WM again the next day. If you fly in to the host city on Friday, you really don't have time to do things like Wrestlecon or Axxess or stuff like that because of how on top of each other the WWE's events are.
I'm STILL a guy who would prefer one night if I had my way and simply just condense the card ("if you make the card you make it, if not tough shyt") but I'm more accepting of a two night show now that I've experienced it. It obviously gives WWE more money and like someone alluded to, the WWE can more and more make it more like a festival.