Firstly, I want to point out that the switch to vaudeville in psychedelic music in 1967 is specifically a British thing. Psychedelia in 1967 in the U.S. - The Doors or Jefferson Airplane, for example - usually comes from a folk/blues kind of background. And there was also plenty of British psychedelia of the era that also was more folk/blues in musical background (e.g., Cream's 'Sunshine Of Your Love'), or with classical influences (e.g., Procol Harum's 1967 'Whiter Shade Of Pale'). When Jimi Hendrix asked you to excuse him while he kissed the sky, he was coming from a point of view somewhere between Jefferson Airplane and Cream.

Which is to say that psychedelia generally works by taking an established sound and subverting it (for example, The Orb's 1991 album Adventures Beyond The Underworld subverts dance music in a psychedelic kind of way, and Miley Cyrus's Dead Petz album psychedelically subverts current mainstream pop). This of course is something like the nature of a psychedelic experience - it overlays new perceptions on top of regular experience.

Additionally, English music hall-influenced psychedelia of the period was not especially popular in 1967, as far as the charts go, even in the U.K.. Instead, there's quite a lot of adult-focused middle-of-the-road pop at the top of the charts in 1967 - Englebert Humperdinck had two chart topping singles - and some light post-Beatles pop - e.g., The Foundations' 'Baby Now That I've Found You' or the Monkees' 'I'm A Believer'. The Beatles by 1967 were sui generis, and they could get away with music hall psychedelia, or long tracks based on Indian classical music, or weird drug music. Many of their teen fans were still a little confused by their musical choices of late (thus the success of The Monkees, who replicated their earlier sound), but the Beatles were able to bring an audience with them to places they didn't necessarily envisage going. Other bands had to work with what audiences wanted, and what audiences wanted six months ago might not be what they want today.

As far as English rock music with a music hall influence goes in the charts in the mid-1960s, there's several examples pre-psychedelia - music hall was very much the music of many a rock star's childhood - George Harrison's turn to the ukelele definitely comes from the music hall star George Formby, for example. And so it's probably inevitable that some English groups would be influenced by it.

The most obvious example is a British Invasion band from London, Herman's Hermits. Their 1965 tune 'Mrs Brown, You've Got A Lovely Daughter' - their first #1 in the U.S. - has a plink-plink shuffle beat that is very reminiscent of music hall. Herman's Hermits knew where their bread was buttered, and they followed that up in the U.S. with a cover of a 1910 music hall tune, 'I'm Henery The Eighth, I Am': it was also a #1 hit (the song was included on an EP with 'Must To Avoid' in the U.K., which reached #6). In 1966, Herman's Hermits even covered George Formby's 'Leaning On A Lamp Post' - the archetypal music hall song - for a 1966 top 10 U.S. single. Herman's Hermits appear to have been concerned to not be too old-fashioned for their teen audience in the U.K. - 'Henry VIII' and 'Leaning On A Lamp Post' were not U.K. singles despite their U.S. success; it likely means that what was old-fashioned and daggy in the U.K. was instead charmingly British as far as the Americans were concerned.

Another English band with an obvious music hall influence is The Kinks, who started their career making dirty garage-y rock'n'roll - e.g., 'You Really Got Me' in 1963. However, their late-1965 single 'A Well Respected Man' saw a successful change in their style to something more melodic, with complex harmonies, and it had some fairly obvious musical hall influences. These music hall influences expanded over the next year in singles like 'Dedicated Follower Of Fashion' and 'Dead End Street' (and in other tracks like 'Mr Pleasant').

Similarly, the Beatles themselves made the switch to vaudeville before 1967 and 'Penny Lane' and Sgt Peppers - 'Yellow Submarine', from 1966's Revolver is very music hall, as is 'Good Day Sunshine'.

However - yes, there was definitely a flowering of psychedelic music hall-influenced pop in 1967 in the UK, everything from 'When I'm Sixty Four' to The Pink Floyd's 'See Emily Play' to 'Hole In My Shoe' by Traffic. The reason for this, of course, was that psychedelia is of course about psychedelic drugs, and one's experiences on psychedelic drugs are influenced by one's mindset and the social and environmental setting. And many interpreted the altered perception of a good LSD trip as being somewhat innocent and childlike.

The Beatles certainly interpreted the trippiness of LSD as being somehow childlike; Lennon's syntactically correct nonsense lyrics for 'I Am The Walrus' hark back to Lewis Carroll, and there's plenty of Through The Looking Glass imagery in 'Lucy In The Sky With Diamonds' (which, despite the band's famous denials, certainly wouldn't have sounded like that without the band's LSD experiences). 'Penny Lane' and 'Strawberry Fields Forever' were meant to be songs about nostalgia for the Liverpool of their childhoods.

In this context, it's not surprising that the music-hall song is a staple of the 1967-era psychedelic pop album; if psychedelia evokes childlike wonder, and music hall was the music of many a British rock star's childhood, it's no surprise that a psychedelic music hall was a thing.

50 years later, the music hall influences of psychedelia perhaps seems a little bit odd/counterintuitive. But in 1967, magazines like Rolling Stone had not yet retrospectively canonised the heavier, more out-there psychedelic rock of 1967 as the height of good music. The likes of 'Purple Haze' or 'Tomorrow Never Knows' or 'Sunshine Superman' were not yet in the rock'n'roll canon; they were basically just pop songs following the fashions and technological advances of the times. In 1967, nobody really knew what they were doing yet, because the currently accepted code for what makes something psychedelic - sitars and drones, and crazy vocal and guitar effects, etc - hadn't really been set in stone. In this context, music hall psychedelia made as much sense as anything else, because of its feeling of childhood.