I'll offer my quick thoughts on this trade:
1) Pomeranz added a cutter this year (sorry if this has already been posted)
http://www.fangraphs.com/blogs/drew-pomeranz-now-with-50-more-pitches/
2) The cutter dramatically changed his profile, and has allowed him to induce lots of weak contact with a lower than average BABIP.
3) Pomeranz is performing at an elite level, is young, cheap and controllable for the next several seasons.
4) No matter how good Espinoza becomes, he's 18, and he's 2-3 seasons-at best-away from appearing in the majors, much less producing at a competitive level there. It also bears noting that Espinoza is struggling in A ball. That doesn't mean that much, but it certainly doesn't mean he's ready to fly through the minors to Fenway in the next 12 months.
5) They address the single biggest need on the team without disrupting the current roster, OR taking on a terrible contract with lots of cash left on it.
6) David Ortiz is in his final season, and the chance to get the man into another October tourney trumps the other considerations.
That last bit says it all for me, and possibly for DD. I'm not saying it isn't short sighted, or that there isn't risk associated with taking on Pomeranz for a huge upside guy in Espinoza. There is, and Pomeranz can crater, get hurt, or just not perform in Boston, and it wouldn't surprise anyone. However, even with the risks inherent in the trade, I'd make it 10 times out of 10 given the circumstances of this team, and with Ortiz' situation. I'm more than willing to suffer the slings and arrows of those who adore the Red Sox farm system-I'm a prospect lover myself-but the reason you have a farm system sometimes is to get guys like Pomeranz when the situation calls for it. There aren't any other starters on the market (or in the system) who are lock solid bets to be productive after a trade, and the only guys I'd say I'd feel very confident in acquiring without risk are guys like Sale and Fernandez, neither of whom would have been available for a single Espinoza. Everyone else: Hill, Santana, Hellickson, all the Rays arms-they all have risks for various reasons, and all of them make more than Pomeranz and/or are not controllable as long as he is.
Sign me up for this deal. Get Papi a 4th ring.