I don't know about the citizenship piece-- I think when we sailed last fall, they said you could self-assist IF you didn't have to go through customs. Maybe they have changed this?
We self-assisted, and it is DEFINITELY the way to go. We sailed out of Baltimore and live about an hour and a half north, in PA-- we were back in our apartment by 9:30 AM. It was the smoothest, most uncomplicated end to a vacation that I have ever had.