IMO, there's no easy way to improve the team for 2014. You look at their lineup, and it's filled with guys in roles that make sense for them, and they really produced at a high level. Their LF production was near the top of MLB. Victorino was a 6.2 bWAR player. Salty had his best offensive season and there just aren't many better hitting catchers out there. McCann could be one of them, but even that's no guarantee moving forward. Pedroia wasn't at his best, but he was still very good (116 ops+, 6.5 WAR). Ortiz was tremendous. Where to upgrade? Then you look at the places where they could lose someone, and the situation gets murkier.
Ellsbury? There is nobody that is available out there that is likely to give you what Ellsbury did in 2013 (114 ops+, 5.8 bWAR). I mentioned Salty already. Napoli gave them a 129 ops+ and 4.1 bWAR. Those guys don't just grow on trees and become easily available.
The two most likely places for offensive improvement, to me, come at SS and 3b, where Boston's production was below average. Bogaerts has the potential to be a real upgrade at SS, and a full season of Middlebrooks - even if he just gives you a full year of what he gave you in 2013 - also represents an improvement. Compare Middlebrooks' 2013 projected over 595 ab compared with the 595 ab the Sox got from 3b in total last year (which obviously included Middlebrooks' numbers):
Middlebrooks: 70 r, 29 hr, 84 rbi, 253 total bases, .696 ops
Sox 3b in 2013: 70 r, 20 hr, 79 rbi, 235 total bases, .683 ops
So it would be a little improvement at 3b.
You're not likely to improve on Napoli's numbers at 1b or Ellsbury's in CF.
Pitching? You can hope for a full season from Clay, and hope Lester's postseason run and otherwise solid 2013 season carries over, and maybe his era drops to the low 3's. Lackey probably can't pitch much better. Doubront may continue to improve, but I don't think the odds are good that Peavy improves upon his 2013 season. And no way Uehara can pitch any better.
So I'm not saying that there isn't room for this team to improve - just that there's no easy way to do it, no obvious path to improvement. Or even to maintain the status quo.