I don't know if this is my "one thing", but it hasn't been mentioned yet, and I think it would make a pleasant difference:
Train all employees and contractors to remain in character! Give them a constantly-tweeked list of ad libs. Teach them to be more than 21st Century people in 19th Century costume. This includes ride operators, shop clerks, custodial staff, and everybody else. Practice with them ways in which they may greet one another when passing in the City, ways to publicly interact with peers, visitors (adults, kids, teens, elderly). Give them permission to have a little fun on their way from one place to another. There's no need for a scheduled show with characters on the square when little interactions like these are allowed all the time everywhere.