I know with bass strings there are people who like them brand new, people who hate them brand new, and people who like them old and gunky.As someone else said in another thread, isn't it funny how "burn in" always results in improvements in sound? You never hear anyone say: they sounded great the first hour but crappy after 100 hours! Sorry, but I am skeptic too regarding appreciable and objectively measured changes in sound after burn in.
My dad often changes strings couple of weeks before a concert, and some of his buds change em before every concert(my dad plays hard and they tend to stretch/snap alot during first plays)
But I have not heard of any one changing speaker cables weekly or monthly.. If burn in changes the characteristics of the metal there must be someone who prefers Virgin metal.