Is Siddhartha’s near-suicide an important step on his road to enlightenment? Is it an important step on the road to enlightenment?

Yes, I believe it is. He dreams of Kamala's songbird, that it's dead, and without thought he throws it into the street. He sees the death of the bird (the way he imagines it in his dream) as the loss of his own goodness. He's appalled at himself, seeing himself as something not worthwhile, as meaningless. These are the feelings that lead him to desire his own death; they lead him to the river....... and there he hears the sound of the water, the sound of Om. At that moment, he knows that he doesn't have to be what he believes himself to be, and he is willing to go on and continue his journey.