Sox marketing should be looking north for ideas, and maybe some employees to steal. I'm not talking about the Cubs, I'm talking about the Brewers.
The similarities between the teams are strong. From 2005-2012, both teams have been to the postseason twice (obviously once with more success by the Sox). They've had roughly the same number of winning seasons (one more for Sox). They've averaged a similar number of wins through those seasons (two more for Sox/year). While Milwaukee's market is small compared to Chicago, the economies have been similar recently. Both teams play in suburban style ballparks in the midst of lots of parking lots without a "Wrigleyville" type of environment. The Brewers have an advantage in that they play indoors in April and May if necessary, but have an offsetting disadvantage in that Milwaukee doesn't have nearly the corporate presence that Chicago does and their fans are probably traveling farther to the games.
Despite all the similarities in performance, the Brewers have averaged over 400,000 more fans per season than the Sox. That includes the World Series and following season for the Sox.
They're doing something right up there.