I consider Tom Petty to be a vastly superior artist to Britney Spears. She has far greater commercial appeal however and her music is worth more today if you're selling a catalog. The same would factor in to selling the Dylan catalog. Dylan's music is not very popular with young people and will not be very popular in the future (see: Elvis, Cher, Neil Diamond, Clapton, Madonna, Whitney Houston, Rod Stewart, Chicago, etc; their music doesn't sell at all like it used to), although I'm sure it'll be redone endlessly. Do young people care about Simon & Garfunkel? Not in the least and they won't tomorrow either. That music will all fade by the year, relegated to a small fraction of the interest it once had, as the primary generation or two that listened to it die.
After 60 years Dylan has sold less than the Backstreet Boys. He produced relatively few hits compared to other renowned, popular artists. His style of music doesn't lend itself to vast commercial success. Someone will pay a premium to acquire his catalog because he's such a great artist and it's a large & influential catalog, however there is a practical limit to that.