Granted, Crabtree had a great season, but we don't depend on the WR position that much for production...perhaps less than any other team. In addition, the acquisition of Anquan Boldin essentially fills the same role as Crabtree -- the only knock on the Boldin trade is that Boldin does the same thing that Crabtree does.
Add in a bunch of speedy WRs and Patton -- and Manningham perhaps by the beginning of the season...and we're fine.