I certainly think that there are many benefits to spirituality on mental health. It is not necessary to be part of any organised religion or faith group to gain benefits. Spirituality can give a focus and a meaning in your life and can give you a sense of acceptance and belonging. Many people with mental health problems often feel like they are on the "outside looking in" and its a lonely place to be.
Spirituality can often become a focus of a person's life during times of emotional stress, such as in times of bereavement. Often this is a time when people seek answers to life after death and why we should suffer loss of any kind. Spirituality looks to finding harmony with the universe, it looks for a way to balance the feelings of "why?", sadness and anger.
Connecting with the spiritual is a deeply personal experience and can lead you to recognise that when you hurt someone else you are in fact hurting yourself. When you lend a helping hand to another, this also aids you.
One of the unique aspects of spirituality is that it spans across all cultures and includes those who do not believe in a god or higher being. Religions are about community based worship and that too sounds like a benefit, however religions are often a source of intolerance which is certainly of no benefit to those with mental health problems and do not need to continue feeling like they are on the outside looking in.
Many practices such as yoga and Tai Chi can offer you discipline, a healthy body and a healthy mind as well as being very relaxing and focused. Some aspects can lead you to connect more with nature and fresh air is essential particularly those with depression. Ritual can offer the benefit of providing structure and reading literature on philosophy can offer fresh thinking to a negative mind. Find out what works for you, what feels right to you.
From my own personal experiences I have found that it has improved my relationship with myself and with other people. It has given a whole new meaning in my life and can help me to live with myself. I still have a long way to go in my recovery and many issues to be worked out yet I feel that it is spirituality that has kept me alive.