I hope no one minds my pulling out an old discussion, but I was intrigued by the comments and ideas you've presented here. I wonder though why no one actually quoted from Columbus himself.

“God made me the messenger of the new heaven and the new earth, of which He spoke in the Apocalypse of St. John after having spoken of it by the mouth of Isaiah, and he showed me where to find it.”

His writings are filled with these kinds of ideas. He made himself a scholar of the scriptures (the Gutenberg Bible was published about the time Columbus was born) and had studied the scriptures extensively. His studies led him to the idea that the gospel of Christ needed to be preached to all the world. His belief would have been that baptism in the gospel of Christ was the only way to heaven and as such should be offered to all. And the way to offer it to all in the 15th century was by ship. He also says in a letter to the King and Queen of Spain:

“With a hand that could be felt, the Lord opened my mind to the fact that it would be possible to sail from here to the Indies, and he opened my will to desire to accomplish the project. This was the fire that burned within me when I came to visit Your Highnesses. … Who can doubt that this fire was not merely mine, but also the Holy Spirit who encouraged me with a radiance of marvelous illumination from his sacred Scriptures.”

Yeah, he could see that there would need to be some “civilized” would required a governor and who better? And if the natives were some kind of wealthy that would certainly benefit Spain. But his main motivation, in his words, appears to be that he believed that God wanted him to go.