The Yankees need to stop worrying about trading Nady or Swisher. They wouldn't be able to get value for them and with trading even one of them you would create a hole. The so-called crowded outfield corners are really just about right when you look at season as a whole.
Damon has been injury prone in the past with his quads and he may be called upon to play center from time to time, Matsui is not as mobile as years past and will be mostly confined to DH, Nady is your everyday right fielder, and Swisher is a bench utility player and pinch hitter that also adds a bit of depth to centerfield. If you trade Nady you lose about 60 hits and some RBI if Swisher's bat doesn't come around.
The bullpen doesn't need shoring up, another veteran would be nice but, not necessary. Nady's bat on the other hand is irreplaceable, short of signing an expensive free agent. There is a lot of talk out there of a much needed bat to supplement Teixeira in replacing Abreu and Giambi, so why get rid of a guy that hit .270 with 12 HRs and 40 RBI in 59 games? Nady is a veteran of New York having played with the Mets and now part of a season with the Yankees and he would be hard to replace.
Swisher getting added makes total sense, the Yanks traded Wilson Betemit, whom I really liked, so they make room for Cody Ransom a little older but, power-hitting utility infielder. Swisher, who hit 24 HRs last year despite batting .219, also adds pop to the line-up. Those upgrades are great offensively and give your bench much more power than it has seen in the last two years. Trading Nady or Swisher would weaken your bench.
Defensively the Yankees need Nady and Swisher to ensure a sound outfield. Abreu was only credited with two errors last year but, watching the games you could tell he was a far cry of his former Gold Glove year.
Nady and Swisher add depth and keep Austin Jackson from being pushed out too early. Yankee fans, myself included, are an impatient bunch and have a reputation for hearing good things about a prospect and wanting them in the field ASAP. (Hughes, Kennedy, Russ Davis, Domingo Jean, Brien Taylor and the list goes on).
The Yankees as an organization and as a fan base demand excellence and they expect it from top to bottom. This is why the Nady and Swisher trades are being talked about because if the Yankees can get a bigger, better deal then they will jump on it in order to:
1. Make Nady's arbitration someone else's problem and
2. Bring in a pitcher or outfield prospect to add depth/youth/speed to the lineup. My advice to Cashman would be patience and make sure that you don't bite on a guy like Cameron who has already seen his best years, as the Yankees have done many times before.