Beane gave up building from within years ago - especially position players. I don't think he drafted a single starter not on the pitching staff on this years team.
Billy Beane is clearly going all in this season, but at little risk. He hasn't forgotten that he started a combination of Bartolo Colon, Jarrod Parker and Sonny Gray against Justin Verlander/Max Scherzer in games 1 & 5 in 2012 and 2013 and lost all 4. He needed to counter and has with this deal.
Cespedes was nearly dealt this offseason to Arizona and wasn't - I think because of the Trumbo pickup. Maybe Beane is forgetting that he also lost game 5 because Cabrera hit a HR and the A's didn't score at all, but the truth is he knows he needs to lower his runs against, not his runs for, to avoid the one game playoff (though I really don't think Anaheim can catch them, but he's worried enough that he had to make a move.
Remove Cespedes' run production for Gomes and they're still +135-140. Now replace the 5th starter (or Hammel) with Lester and it's probably closer to +145-150. I'm not seeing the huge risk in 2014.
Cespedes wasn't going to play for the A's in 2015 anyway.
Boston on the other hand, gave up on 2014 and have made themselves much better for 2015.