I don't know how much was spent on warfare, but I do know that right as Spain was becoming an economic super-power on cheap, unlimited silver they were also violently exiling all the Muslims and Jews in Iberia, and it just so happened that the Muslims and Jews who had been there for centuries constituted most of the non-agrarian economic base of the region. So in their religious zeal to create a purely Christian Kingdom they were kicking out or killing everyone with a skilled trade or a university education, essentially enforcing a massive and long lasting brain drain on themselves. And once all those people were exiled or killed the Spanish leadership never effectively replaced them.