If it's a clear day, sunny and all that, then the view from the water would be quote nice, as would the view from the Empire State Building. The half circle line tour is probably the best way to go, you get the narated tour with the trip.

If you are into theatre or classical then there is still time for tickets to a play, opera, or carnegie hall, lincoln center, something like that (all of which could be done in the afternoon too).

If it's sports, the Yankees are at home, tickets may be still available for the afternoon game against Detroit, though maybe not, you may need a scalper.

The Tartan day parade

http://www.pipefest.com/

will be going down 6th ave, nothing like a bunch of men in kilts to start off a vacation. If it ever stops snowing the tulips and forsynitha's should be in full bloom at the Botanical Gardens, and the circus is in town then.

Oh, by the way, you won't get mugged. You watch too much TV

Consider an early morning trip on the hop on/hop off busses to get a feel for everything, then spend your day looking at what you want to do. Consider Chinatown for Dim Sum for lunch and pastry in little Italy (right across the street from one another).

If you are staying at the EWR Hilton I don't believe you need to take the airtrain. They will shuttle you to the newark train station, and from there just take the train into the city. Penn Station is an easy walk to Times Squuare if that is one of your destinations.