When asked about how the blessing power of holy objects or holy beings benefits us, the great Tibetan master Lati Rinpoche explained how the power of the blessing depends not only on the power of the buddhas but also on one's own faith. However, because of our ignorance, obscurations, and negative karma, we cannot perceive the Buddha's mental body. So, it would seem that through the force of their compassion, skillful means, and past vows, the buddhas must manifest in whatever forms beings can relate to. One might say that these holy objects are like hooks, and by relating to them we connect ourselves with the powerful crane of the buddhas' qualities, allowing ourselves to be lifted up. One other point on how holy objects like prayer wheels help one to develop positive qualities in the mind is worth noting here.
Buddhist teachings emphasize how everything comes into being based on causes and conditions.
And success in developing positive inner qualities clearly depends on many causes and conditions, including environmental factors. One Tibetan analogy notes that when a clean cloth is placed over a dung heap, it will gradually come to smell like dung, while another cloth placed over incense will come to smell very nice. For anyone interested in meditation, this is not a difficult point to prove for oneself experientially. Many people have noted how having a prayer wheel near them helps them to meditate more effectively or to more easily develop positive states of mind. Though Tibetans may begin engaging in the prayer wheel practice based on faith, I suspect that most continue to engage in it based on their own experience of its leading to more peaceful, joyful, and virtuous mental states.