I worry about Lincecum's body holding up, for one. I learned with Pedro Martinez that scouts usually know what they're talking about when they say that a guy's body may not hold up for the long term, and with Lincecum's velocity dipping for three straight years (though it picked up a mile this year) you wonder if that strange motion isn't going to screw his elbow up eventually. And trading for him would make no sense if you aren't going to extend him, and he'll require lots of years and lots of money.
The other issue is that you're paying a premium in players for a guy who may not be as effective in the AL East. The NL West is very forgiving.
All in all, i'd keep my offense intact and go for a Buehrle/Jackson type while focusing on the bullpen, which is a problem yet again, and get a pitching coach that forces those idiots to stay in shape.