Interesting question. I am always surprised when at Dodger Stadium, I hear fans often say "I didn't know the Dodgers came from Brooklyn" when they show old footage on the big screens. Growing up in LA, I always considered them just LA, until I spent time living in NY and grew to appreciate the Brooklyn history and what the team meant to the borough. I think the one thing that will keep collectors and fans interested in Brooklyn is the history of Jackie Robinson. People collect Ruth and Gehrig and a whole host of others having never seen them play, and Jackie is such an important part of history that he will keep the Brooklyn Dodgers in focus.
I also collect items related to Jackie and the '55 Dodgers. One of my favorites is below, a 1955 Yearbook signed by the whole team, and signed "to Irene, from Happy Felton".
Rick
1955 signed Dodger yearbook for posting.jpg