I live in NYC, and have been to Ground Zero ONCE, when working with the Red Cross on the 1st anniversery of 9/11.
Take this as just one guys opinion - I don't want to see it. You will see folks profittiering from it - I don't like it. I lost 2 people I knew that day. I've become good freinds with a guy who lost his brother in law that day. I don't mind you going, but please remember and respect what happened that day. I work a few miles uptown, and I can still remember the smell (you could smell it at my house 11 miles away)
If you down there, I'd actually say SKIP the Statue of Liberty tour!!! Huh? If all you want to do is see a GREAT view of the Statue, walk down to "the Battery" (southern most part of the island - about 1/4 - 1/2 mile from "ground zero") and hop on the Staten Island Ferry - one of the best bargains in NYC - it's free!! It goes RIGHT by the Statue
Go see Central Park - go over by Tavern on the Green, see the sheep meadow, maybe go to the zoo, walk over to the Metropolitan Museaum of Art. or The Museaum of Natural History (opposite sides of the park at about 80th st). See Rockifeller (sp) Center, catch a Yankee Game, find a GOOD Resturant for dinner, have that slice of Pizza (NYC has great pizza - want to start an argument - ask folks where the BEST pizza is) - do NOT be afraid to take the subway - it's the fastest way to get around, and believe it or now, we WILL direct you if your lost - we can usually tell if your a tourist, and many (Most?) of us understand. Maybe go to Times Square - it's NOT the Times Square of old, but more like the Disney version of the same
The list I gave you will take well more than 48 Hours - pick and choose