Yeah it's a good idea to continue the work on Manhattan and a shapefile is welcomed because it's not rewarding to see one's building on the river... Updating the wish list should be a good start :
http://wiki.flightgear.org/Landmark_Wish_ListIf there is a building you want to see, write it there if you don't know how to model your building.
Boeing : To have the latest scenery buildings, use Terrasync so that it upload your scenery when you fly above it. However, I don't know how to update shapefiles...