So who got the better acquisition, the Seahawks or the 49ers? I'd argue that the Seahawks got the better player, but they paid a king's ransom for him, giving up multiple draft picks (including a 1st rounder) to get a player who only has one-year left on his contract and wants to be paid big-time $$$. With Harvin, they have a well-rounded player (when healthy) that can return kickoffs, play slot receiver, and run the ball out of the back-field.
As for the 49ers, they got the better 'deal' in terms of value by only giving up a 6th round pick. Anquan Boldin, at 32-years old, is on the back side of his career, but he's still good for 60+ catches and 900 yards. He's a reliable possession receiver that you can count on in the clutch (see Super Bowl film).
I still think the 49ers need to find a deep threat (easier said than done), but this move gives the 49ers valuable depth in their perennially banged-up receiving corps without having to give up much in return.