The comments that you have made about the Beach Boys, others have made on this site about the Beatles and Elvis Presley. Though whether it is the Beach Boys or any other musical act that is the subject of the acclaim, I believe that is essential to place the musical act in its historic context.
When the Beach Boys first charted a Cash Box Top Single (1963) with 'Surfin' U.S.A.' (#16), we should look at the state of pop music as represented by the Top 5 singles for that year: 1) Limbo Rock (Chubby Checker), 2) Go Away Little Girl (Steve Lawrence), 3) End of the World (Skeeter Davis), 4) Blue Velvet (Bobby Vinton) and 5) Telstar (Tornadoes). The Beach Boys were making different music ... music 'realized in energetic melodies, cheerful repetitions, and magical harmonies' which captured early sixties California life. And that was the formula for the group's first dozen or so albums.
With Pet Sounds, the move was away from fast cars and California girls to an exploration of the mind. Drugs and psychedelia were just down the highway in San Francisco. It may help to view Pet Sounds as a symphony with complex orchestrations. Songs like 'Wouldn't It be Nice' and 'God Only Knows' and 'Caroline, No' and 'Don't Cry, Put Your Head on My Shoulder' ... are not only a break from the commercial formula that the Beach Boys had been following, but arguably stand heads and shoulders above what any other group was doing at the same time both musically and lyrically. This music was possibly the equal to what the Beatles were creating with 'Yesterday' and 'Eleanor Rigby'. It certainly holds together 50 years later.
I was 9 years old and a Brooklyn-ite at the time when all this was going down in 1966 and I can tell you that the Beach Boys were as important to the musical culture as the Beatles, Dylan, Simon & Garfunkel, and the Rolling Stones were. Hendrix and Cream and Woodstock and Altamont and the loss of innocence were yet to happen.
I am a major fan of 'Pet Sounds' and it is not because of nostalgia. I invite you to listen to the album and listen closely and listen several times and listen to the album as a single piece of music and then judge. Use real headphones, not $5 buds. Get the SACD version. If you don't get the beauty and magnificence of both the structure and execution of the songs ... you don't get it. Certainly no crime. It doesn't mean that it is not there though.
Credit to Lillian Roxon's 'Rock Encyclopedia' (1969) for the Cash Box statistics, as well as help in organizing my thoughts.
Rich