The signing is complete and there is no looking back now, Nick Swisher is an Indian and will be one through 2016 (possibly 2017). At this point everyone knows that he will be making $56M over those first four seasons with an option for the fifth. What we don't know is what he will produce.
The first thing to discuss is Swisher's age. He is going to be 32 in 2013 and playing in his tenth professional season. He has been incredibly durable over that time, averaging more than 150 games since 2006. He has produced at a pretty even level throughout that time, but did have a notable peak in 2009 and 2010 (age 28 and 29 seasons). It is likely that he will continue to slow as he ages, with his numbers dropping all over the board. Don't expect more than 20 home runs from Swisher again or a batting average over .275.
The second thing to look at is the Yankee effect. Simply by being on the Yankees, playing with that short right field and batting before or after some of the greatest hitters in baseball history can do a lot to help your stats. This is one of the reasons players can't be evaluated using regular statistics as these numbers won't correlate to other teams.
Since 2008 (the year before the Yankees bought a World Series), the Yankees have had five starting players leave the team and go on to play elsewhere. These players, Bobby Abreu, Jason Giambi, Johnny Damon, Melky Cabrera and Hideki Matsui, all had significant trends in their numbers after leaving New York. While most of these players were older than Swisher and past their prime when they left, the fact that Cabrera is included and has the same trends shows that it isn't simply a matter of age.
What to Expect from Nick Swisher
Burning River Baseball | Jan 28