FOR TWO DECADES, the Tribeca Film Festival has preserved more than a trace of its improvisational origins. Conceived in 2002 as a response to flagging creative energy and property values in zip codes 10007 and 10013 in the aftermath of 9/11, the festival projected an image of New York as a filmmaking hub where moviegoers could mingle with and size up the products of directors and actors like festival founder Robert De Niro, whose offices were and still are in TriBeCa. It was kind of homey, even if you lived forty-five minutes away by subway. The lineups were eclectic—a smattering of big-star