I agree with Nomar. This would be an odd trade for Boston. While ARod is an upgrade over Nomar, he isnt worth the huge increase in salary. It just doesnt make sense to trade away one of your best players for someone that makes more than twice as much and plays the same position. What they need is another starting pitcher and bullpen help. 12mil will get you a good FA pitcher like Pettitte or Bartolo Colon.
Forgot to add that if Texas will eat some of ARod's salary(more than 5mil/yr) it would be a very different situation. If thats the case then it would be an excellent trade for Boston.