Easy to say in retrospect but not taking Manny Ramirez off waivers in August 2004 came greatly to grief.
Since 2005 Manny has 120HR / 402RBI / .301 BA / .560 SLG. He's not A-Rod who is 160/472/.311/.595.
But in the postseason since 2004 Manny has hit .344 with 24HR and 64RBI. A-Rod, in comparison, hit .159 with 4HR and 9RBI. To be honest the Yanks may not have made the postseason 2004-07 without A-Rod's production.
Most importantly there likely would not have been any World Series wins in Beantown and probably an additional one for the Yanks in 2004.