I dabbled in the New Age in my late teens before a powerful conversion experience to Protestant Christianity.
I have seen New Age be both a good influence in some peoples’ lives, and a very dangerous influence in others. It can be a good influence when people who have no religion become aware of spiritual matters and learn to pray and see God in the world. Such people can be respectful of Christianity. However it can be a very dangerous influence when people start to crave mystical experiences and occult powers, or when a Christian compromises their own faith for New Age beliefs and practices. Frightening examples are the Protestant ministers who preach the Feminine principle in God and Catholic retreat houses which set up New Age oriented retreats.
Another problem with New Age is when it becomes a rejection of all reason and scientific knowledge. Such people can become very, very confused and incapable of rational decisions.When this happens I believe that the atheist or agnostic can be better off.
An example of this ambivalence is a Dominican monastery I knew which allowed Transcendal Meditation ™ to use their house for retreats for while because they believed it was good for people to take some time quiet time in their busy lives, but eventually stopped it when they took a closer look at TM’s teachings and practices.
This document,
JESUS CHRIST, THE BEARER OF THE WATER OF LIFE, A Christian reflection on the “New Age”, is a very useful resource for an in-depth response to your question. I think it takes a balanced view. Please note, however, that it is a provisional document for information, and not a formal response by the Church.
I agree, in general, with the opinion of C.S.Lewis that you posted.