Real Madrid's spending doesn't worry me at all. First of all, they are overpaying, way too much. You might argue Kaka's fee is worth it, but Ronaldo's is not, it should be around Kaka's or if we're going strictly off of player performances, a bit lower.
Secondly, this was their starting defense last season :
Gabriel Heinze : A walking timebomb. How United got Real to pay 10million euros for him when he was already 29 is beyond me.
Pepe : Never convinced me as world-class, and he's got 6 more games of suspension.
Cannavaro : Gone.
Sergio Ramos : A year ago was one of the best fullbacks in the world, he was shit this season. Heinze rubbed off on him.
If Perez was smart, he'd go for Vidic. But Vidic doesn't sell that many jerseys. We're talking about the defense that leaked 6 against Barcelona at home, and 5 on aggregate against Liverpool.