They said this match will only happen once in a life time, to me it seems as if the WWE has no idea what to put for WrestleMania, so the 'Once in a Lifetime' match turned into 'Twice in a Lifetime' match.
For me I don't want to see Cena/Rock all over again. The feud was built poorly. The Rock is a whack when it comes to cutting promos. He lost the edge he had 10 years ago. He isn't the same guy. John Cena is... well... John Cena, but he really beat The Rock in the verbal game, hate it or love it. He proved that he can hang and actually kill anyone on the mic if he wants to, but a lot of people don't want to believe in it.
Nonethless, to me the rematch is unneeded. As much as I respect The Rock, I don't see the point of this match happening again. I would love to see The Rock go 1 on 1 with Randy Orton (only if Randy turns heel), but that is unlikely to happen.