There was an analysis posted on another Sox board regarding pitchers who pitched very well for one year (eg: Beckett in 2007) and then had an off year or two and their chances of coming back to excel again. As it turns out, those pitchers are few and far between. I think Greg Maddux was on the list, but I can't recall who else was there. The numbers do not favor Beckett coming back and pitching well enough to justify his roughly $16M/yr salary for four years. He has also lost velocity off his fastball, and it seems to have straightened out somewhat over the years. Unfortunately, he is the key to our rotation this year. Lester and Bucky are going to be good, though probably not as good as last year. Lackey will not change much, most likely, and DiceK is a good #5 SP, ie, he sucks and whatever we get out of him is gravy.
The Yankees starting rotation once you get past CC, however, is a joke.