The Inca indeed, did not appear from nowhere. From Norte Chico, to the Chavín, to the Moche, to the Wari and Tiwanaku, to the Andean principalities that gave rise to the Inca, the Andes have a series of civilizations that date, at the very least, to 3100 BC. The figure of the Staff God, a deity worshiped all over the Andes and probably the cultural ancestor of the Inca god Viracocha,
has been found in pottery remains dating to 2200 BC.
I just don't see how animal husbandry is so important, since all those civilizations appeared without any other animals than the llamas in the Andes. In fact, there aren't many horses in the Andes right now. Mules, goats, sheep, sure. Horses and cows did change the lifestyles of plains nomads in the Pampas and the Great Plains. But the Andes and Mesoamerica, the most well known centers of civilization in the Americas, rose without them. I just don't see why horses and husbandry are important? Maybe they presented a slight advantage in warfare (though I'm not even sure of that) but there were literally
thousands of years of civilization without horses. I've always see that argument, and it just doesn't make sense. Horses are great in plains. But in high mountains or deep forests? Not so much. They are revolutionary, but not a necessity.
Yes, most people are conservative by nature. And the American civilizations seemed quite conservative. But it doesn't mean they couldn't adapt, and the Inca and Aztecs in fact represented novel means of political organization. Sucessor states would most likely have improved on that.
Pre-Clovis dates are found all over South America. 30.000 is quite old and most likely a datation error, but dates from 18.000 to 15.000 years ago are entirely possible and are backed by a growing pile of evidence that is ignored by those who still hold Clovis as the first sign of human habitation in the Americas (Clovis culture is dated to 11.000 to 12.000 years ago), but there's a laundry list of sites predating that, further in South America, and you can't dismiss them all as datation erros.
The current model of Bering Strait Migrations is likely all wrong and should be revised.
(note that I'm talking about
human prescence, as in early hunter-gatherers,
not civilizations. The oldest civilization on the Americas found yet is still Monte Chico, in 3100 BC, though there might be older remains)