Usopp isnt a necessity to the crew. He rarly gets a good fight, and is mainly comedy relief. I think he could only gain by going to Elbaf with the giants, makes me wonder why Oda threw that in there. Im a Paulie fan and think he would be a humerous addition to the crew, in addition to of course Franky. Paulie is himself going to be wanted by the government, especially for aiding the Straw Hats, and we already know that the government considers him and everyone else who charged Enies Lobby, part of Luffy's crew. We also know that heis quite strong, if he could hold giants with his ropes. He also has debts so he needs a way to make money. Plus, imagine the scenes between him and Sanji over Nami and Robin's dress.