That may be so, but other than working with pitchers one could make the case that Cash is already at least as good as Varitek is at this point. He certainly has a better bat and is better defensively.
Varitek is also going to want a huge contract through his agent Scott Boras, aka Satan. He might... MIGHT have one more season left in him, but that's it. And his affair with the NESN chick (resulting in the dissolution of his marriage) isn't helping his rep in Boston much, either. It's time for him to go.
I really question if he's got another season left, his bat's definitely gone, and even his defensive skills in the post showed signs of dropoff. I've been defending with co-workers how I'd live with his poor batting for his defense and his leadership, but he was up so much this season when it mattered and choked, his bad bat really hurt a lot of times.
With his affair too, I wouldn't be surprised to see that play into him being signed. Boston's front office doesn't want BS like that affecting the team, and Boston fans won't support a known adulterer so if they feel his social behavior bears enough negative on the club, they'll cut him.