I think this race and the next will be a litmus test on whether or not Lewis can put up a real challenge for the title. (technically up to now even Karthikeyan is in the running to be champ, but realistically, he's not mounting a "real" challenge) He has always won here (other than in 2008, which I believe, if he hadn't crashed, probably would've won anyways) and in Valencia he's typically very strong, looking good for a win (usually) and ending up with very strong 2nd places (he has a 100% record of 2nd places there IIRC).
If Lewis can't beat Seb/win here, or can't beat Seb/get at least 2nd in valencia, then I think Lewis's chances aren't really much of taking the fight on.