What if America was never colonized or even discovered at all?

This is an interesting question. If the Americas had remained undiscovered, Europe would have likely remained much more as it was in 1491 for a far longer period. We can say with confidence it is unlikely the Europeans, who historians such as Charles C. Mann argue had a much less efficient system of agriculture than Native Americans, would have developed such staples as the potato and the tomato. Therefore, such events as the Irish potato famine would never have occurred; although, ironically, without Native American crop imports and innovations, famines would have been more frequent and severe, slowing economic and population growth.
Tobacco would not have come to Europe, as it was brought back from the Americas. More importantly, Europe would have had to do without the influx of such raw materials as timber and fur that flooded in from the colonies. Valuable metals, such as silver, also initially poured in from the New World, and the market for slaves to cultivate such crops as sugar and tobacco would not have existed, so the lucrative and cruel slave trade likely would not have developed.
The Americas brought much wealth to Europe, especially early on. This wealth, coming in the form of raw materials, brought what some historians call the "curse of natural resources" to countries such as Spain. When a nation's wealth can derive simply from selling the natural resources from the territories they own, that country does not have to develop an industrial base.
In Spain, vast wealth was captured by a very small percentage of the population. The wealthy class did invest in the country, but they also squandered a mind-boggling amount of money on palaces, wars, and consumer goods such as costly clothing. When the party was over, the country was left impoverished. Other countries, such as Great Britain, used the resources that came in to develop an industrial base, such as a textile industry, and therefore prospered. Without these American resources, one can imagine that Spain might have done better economically and Great Britain worse, equalizing power on the European continent more than actually occurred.
Of course, all of this is speculative, but without the wealth countries such as England and France amassed through the colonization of the New World, they would have had a much harder time financing the navies and imperial adventures that allowed them to dominate much of the globe. We might today, as a result, have more international equality, and we might, as a world, have benefitted more from the wisdom of cultures that were crushed under colonialism.