Like the staircase, a mantel is a prominent millwork element that may define the style of the house, if not its date. If yours is original and fits the house, wonderful! Be respectful in any upgrading.
For most folks, the business end of a chimney is the hearth that throws off the warmth and the mantelpiece that grabs center stage in the room. For architects and builders, however, almost as important is the chimney top.