Music catalogs are fetching huge deals. Are they overvalued?

In the 2006 book "Northern Songs: The True Story of the Beatles Song Publishing Empire," journalist Brian Southall captured a music industry mantra: "For songwriters and publishers alike, the most important five words are always the same — 'never give up a copyright.'"

For generations of popular musicians who stuck to that philosophy, the strategy is paying off handsomely. Song catalogs from the Baby Boomer era and after are fetching enormous sums from publishers, private equity firms and others looking to capitalize on the music business' recovery.

Bruce Springsteen in December reached a deal with Sony Music Entertainment to sell his master recordings and songs for $500 million. Warner Chappell Music early this month bought David Bowie's songwriting catalog for $250 million. A variety of rights and assets from artists including ZZ Top, Tina Turner and Paul Simon all sold last year.

Trade publication Music Business Worldwide estimated that more than $5 billion changed hands through music rights acquisitions last