I have an interest in the psychedelic underground of the 1960s, and I've recently noted some interesting parallels between Lewis' writings and the New Age culture of this epoch, implying that he might have predated some of it. Most notably:

1) Esoteric space opera. Lewis' Space Trilogy was one of the first works that blended esotericism with cosmic sci-fi (alongside Lovecraft and David Lindsay's A Voyage to Arcturus) - and the amalgamation of UFOs and spirituality became commonplace in New Age movements. In particular, he makes a mention of "Macrobes", demonic entities that pose as benevolent alien lifeforms - and 1969 and 1970 saw the publication of the books "Passport to Magonia" by astrophysicist Jacques Vallee and "Operation Trojan Horse" by the ufologist John Keel. Both of these books suggested that the UFO phenomenon could be originated by the same entities that are known in folklore as fairies, gnomes, demons, etc., that these entities are some form of sentient life on Earth that is older that humanity, and that they are now posing as extraterrestrials.

2) Eclectic mysticism. Though Lewis was a clear-cut Christian, he incorporated many elements of other religious traditions into his works: for instance, he makes use of Lilith from the biblical apocrypha, alongside with fauns, centauri and other creatures from Greek mythology, etc., and in "The Abolition of Man", he references Taoism. After visiting Greece with his dying wife Joy, he also wrote: "I had some ado to prevent Joy and myself from relapsing into Paganism in Attica! At Daphni it was hard not to pray to Apollo the Healer. But somehow one didn’t feel it would have been very wrong – would have only been addressing Christ sub specie Apollinis". The New Age culture also blended elements of Christianity with Paganism and Eastern mysticism.

3) William Blake. I know that Lewis appreciated him, and though he wrote "The Great Divorce" partly as a rebuttal of "The Marriage of Heaven and Hell", he still referred to Blake as a "great genius". And Blake became an iconic figure during the 1960s, due to his mysticism and free love ideas.

4) Barefooting. Lewis depicts a lot of barefoot characters in his works, and lack of footwear usually symbolizes enlightenment and spirituality: this includes Merlin from That Hideous Strength, as well as Lucy Pevensie, Coriakin, Ramandu, Ramandu's daughter, the Hermit of the Southern March, and some others from The Chronicles of Narnia. The hippie and New Age counterculture also engaged in barefooting, for exactly the same reason.

Perhaps there are some more parallels that I didn't notice yet. Would be very interested to hear what you think!