For years, the Pirates followed a pretty consistent strategy when it came to trading prospects and taking on payroll. That strategy was always to defer to taking on money, rather than giving up additional players.
They did this in 2011, when they were barely contenders, and traded for Derrek Lee and Ryan Ludwick, taking on salary and only giving up Aaron Baker in the process. Later that off-season, they traded two lower level wild card prospects for A.J. Burnett, while taking on half his salary, and refusing to part with better prospects for more salary relief.
The 2012 season saw them trading actual players, with Brad Lincoln going for Travis Snider, and Robbie Grossman, Colton Cain, and Rudy Owens going for Wandy Rodriguez.