In terms of keeper. You aren't keeping either Dunn, Fowler, or Bourn with Kemp and Trout obviously your two keepers. Dunn is on your bench and Bourn is an upgrade over Fowler this season. Obviously Bourn gets you more SB, Runs, and Avg, but Fowler/Dunn get you RBI and HR.
Like the other guy said this clears up a roster spot too.
Personally if we were talking player value I would rather have the best player (Bourn), but this trade makes sense for you.