Rey vs. Cara is the only match I'm even going to pretend was going to be good off of that entire list. Plus, Orton vs. Kane is going to be twenty times better than Henry vs. Kane, if you don't believe me, just look at the match the two of them had right before Kane's injury. The diva's match was a downgrade, but that match you mentioned was never set in stone. Any dream of that was shot down over 10 months ago which means the WWE wouldn't have even been thinking about the Mania Diva's match by then. No need to even have a MITB at Mania either, even though I like MITB matches. There's a PPV dedicated to it, and if they're having one at SummerSlam, it should suffice.
So basically, I don't think many people really give two shits about this 'original card' you speak of. Be glad you're getting what you're getting, which is four awesome main event type matches, plus GM Wars, which isn't great, but decent enough.
AND what will still be one of, if not THE biggest Mania in history.