Assuming characters aren't just going to spoil the entire plot of P4 with some end of the match quip I can't see myself being bothered by knowing any of that in advance. I'm more concerned about major plot spoilers than anything else.
And actually, my wife got me a copy of P4 for the PS2. I don't have a Vita and likely won't get one for a few years, if at all, but I was tired of not having finished P3 or played P4 so I've been aiming to get those crossed off my list.