No, it isn't. IF A-Rod stays healthy, I don't think .250 with 20 homers is out of the question. And that's probably top-end production from Headley.
Yankees fans want no part of A-Rod's grand return to NY. But, if he's the best 3B option, he's the best 3B option. And, if you're going to pay him, you might as well play him. If he comes out and hits .198 with 3 homers in April/May, he's justifying a decision to release him. Then, if he goes off somewhere else, the Yanks fans have an even better reason to hate him.