Immediately before this, Dagny had learned (much to her chagrin) that Dick McNamara had inexplicably vanished right before he was supposed to start work on the Rio Norte/John Galt Line. There was no warning, no explanation of why he left, and no indication of where he went. In the aftermath,
It was late when [Dagny] left her office. Outside, on the sidewalk at the door of the building, she paused, looking at the streets. She felt suddenly empty of energy, of purpose, of desire, as if a motor had crackled and stopped... she felt the wish to find a moment's joy outside, the wish to be held as a passive spectator by some work or sight of greatness. Not to make it, she thought, but to accept; not to begin, but to respond; not to create, but to admire. I need it to let me go on, she thought, because joy is one's fuel... She thought: It has taken so much to build this city, it should have so much to offer.
Note that the statement in bold comes to be very significant in the novel later because
the story was precipitated by John Galt walking out of the 20th Century Motor Company and promising to stop the motor of the world (which he did by organizing a strike of the most capable members of society, thus bringing about a global economic collapse and the demise of the Looter governments).
Instead of what she was looking for, she heard a symphony on the radio that sounded like "a long screech without shape, as of cloth and flesh being torn at random... if music was emotion and emotion came from thought, then this was the scream of chaos, of the irrational, of the helplessness, of man's self-abdication."
Immediately after that, she sees the scene you describe. So, rather than finding someone else's accomplishments, she finds a tribute to man's self-abdication and irrationality and a condemnation of the most accomplished members of society.
After seeing these and a couple of other things like it, she reflected on the experience:
What had she hoped to find? - she thought, walking on. These [i.e. the music, the book, etc.] were the things men lived by, the forms of their spirit, of their culture, of their enjoyment. She had seen nothing else anywhere, not for many years.
This stands in stark contrast to Richard Halley's Fourth Concerto, which she listened to when she got home:
The Concerto was a great cry of rebellion. It was a "No" flung at some vast process of torture, a denial of suffering, a denial that held the agony of the struggle to break free. The sounds were like a voice saying: There is no necessity for pain - why, then, is the worst pain reserved for those who will not accept its necessity? - we who hold the love and the secret of joy, to what punishment have we been sentenced for it, and by whom?
So, the book, music, etc. are in stark contrast to the city's potential.
TL;DR It's an illustration of the general cultural decay, an illustration of the fact that people were rejecting that which could offer them joy and life.