This is not to diminish the significance of the 1492 landing. Though Columbus could not really discover a place where people were already living, he did discover America for exploitation by Europe. And, as Robert Frost might put it, that has made all the difference.
Columbus Day now seems to have three distinct identities: It's a tribute to Columbus and the "discovery" of America; a day of ethnic pride for Italian Americans; and an excuse for a three-day weekend when the fall foliage is ablaze.
Since America's founding, Columbus' reputation has varied wildly. He has been revered as a sort of proto-Founding Father whose portrait might be found next to George Washington's in our schoolhouses. And he has been derided as a stubborn bumbler who brought about the deaths of tens of millions.
In fairness, Columbus was an exceptional sailor and entrepreneur who was obsessed, as so many were at the time, with finding a quicker and more cost-effective route from Europe to China and India. He bumped into America because it was in the way.
So Columbus' motivation was self-interest. He did not explore to improve humanity, but he didn't do it to inflict catastrophe either.
A form of the explorer's name, Columbia, has long been used as a poetic name for America and as a feminine personification of the United States. Think of the Columbia Pictures torch lady and the patriotic tune "Columbia, the Gem of the Ocean." There's a statue of Columbia atop Memorial Hall in Fairmount Park, and our nation's capital is of course the District of Columbia.