Bud Selig is busy patting himself on the back for Tuesday's All-Star game ending (Sports Business Daily $$$. I tried to find the original article at MLB.com (the source, according to SBD, and via Google but haven't been successful):
The AL won last night’s game 3-2 in the ninth inning, and Selig said of the format awarding home field advantage in the World Series to the game’s winner, “Did you see the reaction of both teams at the end? The intensity was tremendous. That’s the thing that had been missing. And now we’ve brought it back”
Competitive juices undoubtedly had an effect players' reactions. The context of the winning hit - down to the last strike for the AL - was also important. Without the home field rule, were the players likely to have simply packed their gear and left the field as quietly as church mice? That's doubtful. My guess is the marginal effect of the home field rule was rather small in this particular game.
Having home field in the World Series has been important of late
Will it matter? In the last 20 years, 17 of the World Series champs have had home-field advantage and the last road team to win a Game 7 in the Series was - perhaps appropriately, considering the location of Tuesday's game - the 1979 Pirates.
The team with the advantage gets to play the first two games and, if necessary, the last two at home. But making it to the World Series is an uncertain event from the vantage point of players in the middle of July. Many of the players on both rosters know that their teams will not make it to the post season. For other players with a brighter ray of hope, the probability of making it to the World Series is also very small. Their teams have to make it to the playoffs and then win two series to advance. Then there's discounting (to what extent do players discount the future?).
In a "full information" non-discounting world, the value of home field advantage is huge. But in an uncertain, discount-the-future world, the expected value of home field advantage is much smaller.