The case for him is very good, I agree--our ace, who has been our most consistent starter for almost 7 years, and has been very good postseason. However, consider the following--
1. He can't fix the hitting problem at all, and that problem is by far the more serious one. Lester is having a terrific year, ERA of 2.50, but the Sox have a losing record and Lester is only 10-7.
2. His price tag is high, in all likelihood, high for a long time, like maybe 7 years. Think $24M/year = $168M. That is, I hasten to add, an amount behind the dreams of avarice, and it gets paid whether or not Lester is injured or otherwise unable to pitch. Anyone think he will still be this good for the final three years of the contract?
3. Meanwhile, the Sox just picked up a pretty decent hitting outfielder, Cespedes, who has hit more dingers than anyone on the Sox but Ortiz, scored more runs than any Sox player, and batted in more runs than anyone but Ortiz, and he is theirs for next year as well.
4. Lester is still available for 2015 and beyond. I don't think that will happen because I think he wants a huge contract, but he will definitely be on the market because Athletics can't afford him. Relatedly, I also do not think Lester was available for a non-huge salary last winter.