You can’t turn around these days without bumping into a theatrical production that is little more than an excuse to showcase music that was wildly popular a few decades ago. From Mama Mia to Movin’ Out, Broadway is rife with such shows, and the new season will include new revues featuring the work of The Beach Boys, Elvis Presley, and Johnny Cash. “A quick look at the demographic of the theatre-going public reveals that once again — as in so many other places — the dreaded boomers have a stranglehold. It’s no wonder, then, that producers will try to woo them with material from their happily remembered youth.”