Boudhanath Stupa, a world heritage site, as devotees perform rituals on the last day of Tibetan Losar.
"The stupa, an architectural structure usually housing the cremated remains or possessions of important saintly figures, is considered to be the structural emblem and the most important type of monument of Buddhism" (ahencyclopedia). The destruction of the Stupa not only destroyed the building, but the possessions and remains of important people that represented the culture of the people. That would change the importance of the Stupa simply because you cant rebuild the remains of the figures. The building would still have meaning in itself, but not the way it would before.
"The Mahaparinirvana Sutra (an ancient Buddhist text describing the last days of the Buddha) claims that after the Buddha passed away, his followers divided his cremated remains into eight portions. Each of the eight kingdoms in which the Buddha had lived received one portion of the relics, and a stupa was erected in each kingdom in order to house the remains" (ahencyclopedia).
Basantapur Durbar Square before the earthquake struck.
9-story Dharahara Tower.
"Among the capital's landmarks destroyed in the earthquake was the 60-meter Dharahara Tower, built in 1832 for the queen of Nepal" (Kathmandu). Since the structure has been rebuilt a few times before because of other earthquakes, its hard to say if the rebuilds have affected the spiritual meaning of the building to its people. It was built originally for the queen of Nepal, so the original that was built in 1832 probably had more spiritual meaning then the multiple rebuilds of the same building. It has been changed throughout the rebuilds by making it bigger and smaller.
Dharahara tower, a city landmark, after the earthquake hit.
Basantapur Durbar Square, or what was left after the earthquake.