Been thinking about a line from the TIME review of the GV Box in 1993: "The lyrics were as fleeting as a waking dream..."
It's the "waking dream" part of the thing that is of interest. The LSD experience has been referred to as the "conscious unconscious" and a "waking dream" seems like something along these lines.
Brian's Bio talks of an acid flashback after which Brian remembers, "Loren once explaining that hallucinations were comparable to Zen riddles, mysteries full of meaning."
So the basic idea is: is SMiLE a hallucination with the ability to conjure spiritual enlightenment (a la Zen riddles) via mysteries full of meaning?
The spiritual enlightenment motive is contained in the SMILE BRIAN--AND PULL THEM STRINGS article written by either Michael Vosse or Derek Taylor depending on who you believe. Brian explains the reasons behind the promotion of vegetables: "Health is an important ingredient in spiritual enlightenment." By promoting one (vegetables & heath) Brian is promoting the other (spiritual enlightenment).
Brian's explanation of the "Surf's Up" lyrics includes the following, "He's off in his vision, on a trip. Reality is gone; he's creating it like a dream."
Now here's a line from Arthur Koestler's The Act Of Creation.
"Thinking in pictures dominates the manifestations of the unconscious---the dream, the hypnogogic half-dream, the psychotic's hallucinations, the artist's vision."
Let's add into the mix Frank Holmes' comment about the SMILE SHOP front cover: "The drawing is a surrealistic idea; a visual that is not accessible in conscious reality …" Not only do we get the "surrealist" phrase which is close to the hallucination idea but were also get the hint that SMiLE's art is accessible only via non conscious means.
Van Dyke Parks also gets into this picture through his "dream-escape" GV Box set comment as well as his "don't awaken me" comment from the BWPS tour program.
The point of all this is to indicate that SMILE presents us with images in keeping with unconscious processes, just like with the idea of a waking dream, with the possibility of conjuring spiritual enlightenment.
"Dada" can mean the art form which is close to surrealism & the idea of hallucinations. But "da da" is also what a child calls its father as well as anything containing similar attributes. The child's view doesn't discriminate...neither does the dream or hallucination.
And this frame of mind makes one ripe for the spiritual experience.