It would seem to me that wiping New York off the map, besides the obvious impact on Wall Street, etc would serve little. Of course a more juicy target is inside the Beltway. But, I would say that if the idea is to indeed strike terror into the hearts of Americans, then NY is not the best target. ANYWHERE else is therefore instantly more vulnerable. Of course, lacking a means of delivery other than a ship it limits the target list to major seaports.
Right after 9-11 I was told by an active duty SpecOps officer that my neck of the woods was "safe" because the bin laden network was using the South American drug cartels to get their money. Therefore, the logic went, the terrorists would be reluctant to hit south Florida and risk killing a relative of one of those cartel members. Because not only would that choke off the supply of money, but those guys would seriously HUNT you down and administer the proverbial "Columbian Necktie." NOW....there has been such a crimp put into those networks that it no longer matters if the terrorists P*** OFF the cartels. That leaves south Florida on the target list.
It is my personal opinion that south Florida is at more risk for a chemical attack, rather than a nuke. If I was choosing the target for a nuke, I'd pick San Francisco and the Golden Gate Bridge.
Maybe NYC is a feint, a distraction?