How about Cortez gets beaten by the Aztecs but word gets back to the Vatican about great empires built on jewels and gold and the Pope just finds it too alluring to resist. Maybe he intends to use some of it to rebuild the Armada or something.
Errr...the Armada was 1588; Cortes conquered the Aztecs in 1521. England hadn't even gone Protestant by that point. Moreover, that's not going to give the impetus for a Crusade; rather that would just encourage the Spanish to try invading again (which they would, long before 1588).
The Pope isn't going to call a random crusade across the ocean (although he might officially sanction the Spanish conquest, but he effectively did that already). The 1500s have much, much larger threats to Catholic Christendom running around, even if he wanted to go all Crusadey (the Ottomans are still making gains, and the Protestant Reformation is in full bloom).
Nor would the Spanish want him to do so: they exerted as much control as they could over who and what could be transported to the New World (partially to prevent "contaminating" the natives with heathen or heretical ideas, partially to prevent smuggling); the last thing any Spanish monarch would want would be a horde of foreigners coming over on crusade. The same goes for any other colonial power.