It's hard to say this for sure, because I can't put any reliance on the ticket sale numbers prior to 2013. For the most part, Fenway is pretty full. Their home attendance last year was 36,021 per game. The capacity is 37,731. At 81 games, there would be at most an additional 138,510 tickets you could add (and attendance is probably not total tickets sold). At $200 per ticket (most likely would be far less), that's still only an increase of $27M. There isn't enough meat on the bone for a FA signing to make a financial difference.