But a giant convention center in Queens sounds like pretty much the stupidest idea ever.
Sure most outsiders have a rather Manhattan-centric view of New York city, but that's kind of the point. People who pay to go to New York want to go to Manhattan, or at least have easy access to it. And while we can fantasize about how this will help make Queens extra awesome (I actually don't know this neighborhood so I'm at a disadvantage), convention centers are a lot like casinos. The people who run them want to keep you and your money inside, not wandering around the surrounding streets.