"Valuable" is either quantifiable (in $) or subjective (in terms of the music itself). These sensational articles (and Discogs publishes a few regularly) rarely address what's on the album. I understand the lure of collecting rare music that you love. But in absolute terms, some deviant variant of "Sugar, Sugar" (which I just made up), no matter how much a particular individual loves it, should not be labeled as more valuable than an original Robert Johnson 78 (except to that individual).