If you use WAR, he was worth about 14 million last year. That's pretty nice to have out of a SS. That being said, he will never get market value before he hits free agency. That would be just stupid of the Cubs. That's like Hank Hill car shopping and paying the sticker price for a car. Why pay that when you can get it cheaper?
No way he'd get 5 million in his first year of arby. I think the split is 20/50/80(for three years, of course. With next year being an early year, it's almost certainly going be low, in the 20% of market value range). So if we say that he's been worth 30 million (7.7*4) over 3 years, that's 10 per year. You're looking at about 2 million for him this year. Then 5 for 2014, 8 for 2015. So we're looking at a bit less. Plus he gets this money guaranteed. I think this is a very fair deal. For both sides. Thinking that he would get market value is not going to fair well for you.
I think that the biggest cause of concern is his free swinging ness. He is shaping into a lower part of the order hitter. His BB rate has fallen, while his swinging at pitches out of the zone rate has risen. I mean even if he isn't the superstar bat we all want him to be, he's still a solid hitter and that with good defense at SS is wonderful. I just hope that if he continues this free swinging ness they put him lower in the order(as we get better players and the players we have out perform him), because I know that it will be easy to put him at the top because that's what people want, but it's not necessarily going to be what is best for the team.