Can you tell me about the times Vitthal appeared to Baba's devotees in Shirdi?

Yes, the texts describe multiple instances where devotees experienced visions of Vitthal in Shirdi. Chapter 4 details how Sai Baba promised Das Ganu that Vitthal would appear if the devotee was "full of faith," and it is stated that Das Ganu did receive a sight of Vitthal. In another account from the same chapter, Kakasaheb Dixit had a vision of Vitthal during his morning meditation. When he later went to see Baba, Baba confirmed the vision by asking if "Vitthal Patil had come." The experience was further validated when a seller arrived with pictures of Vitthal, one of which exactly matched the form Kakasaheb had seen in his vision.