What i am noting are inconsistencies in your thought process. In both scenarios, you are exchanging proven MLB players for unproven prospects, but in one scenario, you are exchanging young, cost-controlled players , instead of using already-under control talent and letting go of veteran, in-decline talent to do so. The players you mentioned as possible "trade bait" are players who should be around in 2014 and beyond. Also, them being "only cheap in MLB teams" does not matter to this discussion, because they are indeed cheap when factoring in their production, and this is indeed MLB. Also, this is the Boston Red Sox, not Kansas City Royals, meaning they don't need to trade away premium talent for prospects.
I just don't see how trading away core players for prospects makes sense, when they have money coming off the books and in-team prospects to plug holes. It seems like a scenario where you do something for the sake of doing something.