Smells rather wankish. I would argue that the Armada can over-run a lot of england if it gets ashore, but actually holding down and conquering the nation, now thats another story. In the long term, even a best case Spanish success in 1588 stretches their empire even further, and when things do start to go downhill, bad stuff happens.
Well, anything that has one country control all of the Americas is a wank by definition. At the very least, the Armada would need to seriously weaken England enough to keep them from colonizing anything.