^ I agree, having them one after another would be best because everyone would already be in town. Maybe even people that didn't plan on going to one would end up going to both because they'd already be in the area.

As it is now they might both end up with half full venues. =/

Regarding Date change: I don't think it's impossible. I know they plan a year in advance, but I don't think the venues need to be booked so far in advanced. I would think most of the planning is stage design, getting equipment, getting staff hired, visas, salaries, etc. And of course plane tickets and hotels.
I've looked at venue calendars before and they usually have days open. If not, move to a different venue. And I'm sure all those small local bands don't book a year in advance.

I would think that as long as the band and staff are already going to be in the area then it wouldn't be impossible to move to one day before/after. Say, if they were going to be in the area for a couple days then they wouldn't have to change hotels or flight plans. VAMPS' plans were announced awhile ago so I think that would have given X enough time to adjust ONE show.