No doubt. But consider this...
Youkilis moves to 3B, where his offensive contribution by WAR is magnified. He's a safe bet to reproduce, or even better, 7.1 WAR.
The new 1B need only replace the 4.2 produced by Youkilis last year, which is no small feat, but getting close with a Derrek Lee or Lance Berkman on a short contract isn't out of this world.
The catcher position will be a little more daunting, but also consider the production from the outfield as a unit last year (Drew 2.6, Hall 1.0, McDonald 0.8, Kalish 0.6, Reddick 0.2, Ellsbury -0.2, Cameron -0.3) . It's no large assumption to suggest they will get better aggregate production from that unit even without a big FA acquistion. Just going on the year prior to last year you have this (Drew 4.8, Cameron 4.4, 2.7) and you have the development of Kalish as the 4th OF. While they may not replicate what they got from their catcher, they should easily get if from the OF.
Now, just replacing last year's production clearly isn't enough, they did miss the playoffs afterall. But they've also got the continued development of Jed Lowrie, hopefully a full season of Dustin Pedroia, and a reasonable expectation that the starting rotation should be better (overall).
Fix the BP, and you've got a contender.