During the grape incident with Boss Dharamsee, were other devotees present, and how did their experience differ from his?

Yes, other devotees were present during this event, which served to highlight the personal nature of the miracle. Chapter 35 mentions that Babasaheb Tarkhad, another devotee, was sitting near Baba at the time. While Baba was giving grapes to Dharamsee, he was also distributing them to Tarkhad and others in the group. The key difference was in the grapes themselves. After Dharamsee was amazed to find his grapes were seedless, he asked Tarkhad about his. Tarkhad replied that his grapes did have seeds. This contrast made Dharamsee 'extremely surprised in his heart,' as it confirmed that the miracle was a personal grace intended specifically for him, to address his specific doubts and draw him closer to Sai.