They began to have an underground appeal around 71 til maybe 74. Then Endless Summer came out to make them a mainstream draw again. Continued through 76 with the return of Brian on stage. It seems that they slipped a bit from there. Although never as bad as the 68-73 era. Then in the late 80s with the masterpiece Kokamo

I guess put them on top again briefly. Then I think with releases of the Pet Sounds box set, and Brian's solo tours, there has been a growth of appreciation for the Beach Boys deeper cuts. Although competing against Full House and Home Improvement type things.