I'm still a bit sceptical as to why Barca didn't want him any more but if he's as good as he was when he left Arsenal then he'll do for me.
Because Barca, Real and to some degree Bayern operate on the, we have to buy a big name every year or one of our opposition fans might mock us for being dirty and poor.
Barca/Real have thrown away brilliant players because they want to buy another one, just for the sake of buying a new player. They got rid of Robben, stupid, Sneijder.. less stupid, Higuain.. very stupid, Ozil... bale a pretty big improvement.
Barca have thrown away Eto'o, Ibra and Villa, then you've got Keita and don't forget, Yaya. Valdes is an odd one, he says he wants a new challenge, which is fair enough, but you suspect they really just weren't offering him what he was worth. Best keeper by a mile over the past 5 years, crucial to the team with that woeful defence.
Bayern don't always do it, but then Guardiola didn't seem to have trouble randomly overpaying for Thiago just because he wanted to buy someone. They bought Gotze when they didn't altogether need him, and they bought Lewandowski when they didn't really need him. Ultimately they are getting rid of other players or marginalising some to give those guys game time.
Effectively every season there will be an epic bargain available from Real/Barca as they make room for a new player by pushing a top player out. It's pretty much only Ozil I can think of in recent history that went for an epic fee, more than he was worth, when being shoved out of the door to make room. Higuain wasn't cheap, but is also worth the £30mil. Robben/Sneijder/Ibra/Villa/Eto'o/Keita/Raul, all bargains basically.
Arsenal were nuts not to put in an offer, Man Utd were nuts not to put in an offer, City were nuts not to put in an offer.
If CHelsea manage to get rid of Ramires and bring in a top notch player instead, then Mourinho will have done some excellent team fixing since he joined. Matic, Fabregas, Costa were the big fixes, replacing/removing Mikel/Ramires/all the strikers is what the team needed when he rejoined Chelsea and they've a good job of that so far.