I just don't see how the Red Sox keep Miller, Morales, and Breslow when they have 5 or more righties they want to keep in the bullpen (Hanrahan, Bailey, Uehara, Tazawa, Bard, Aceves, and I'm forgetting a few w/o options). They have to move bullpen pieces as much as we have to move Morse. You can argue Breslow isn't enough in terms of WAR for WAR, but I agree that Morales would be the type of guy you'd expect Rizzo to be interested in - hard thrower, useful out of the bullpen, some good starts in the majors last year as well. I would think a move for one of those lefties makes even more sense for them than making more than a 2 year commitment to Napoli.
A lot is made out of Morse's glove and his minus 28 UZR-base fielding runs over the past 3 years, but about 22 of those negative runs have been run up in the outfield. Napoli has a better fielding component of his WAR on Fangraphs, but a lot of that was run up at catcher, which I think starts with a positive positional adjustment of 20 runs over left. Just looking at their 1st base UZR since 2010, Morse has played 888.1 innings and compiled a -2.7 UZR, while Napoli has played 1040.1 innings and compiled a -2.6 UZR. While there probably are not enough innings to say those are measures of their true talent, what I think you can say is that is that the UZR at first base does not decisively point to one or the other being a better fielder.
As a fan of both the Sox and the Nats, I would love the Sox to walk away from Napoli and deal Morales for Morse. I just don't see a $26MM - $39MM commitment to Napoli over multiple years to be as much in their interest as a $7MM 1 year commitment to Morse (less whatever Breslow or Morales makes). If I were the Nats, I might expect a little more than just Morales, but that's for Rizzo and Cherington to figure out.