I believe it absolutely is more desirable in most every case but I never seen a consistent % value increase.
It also depends on the pedigree. And the comic. Some of the less collected comics can get a bigger bump just so someone can say they have a Church or Okajima comic.
That's a good point. Some of the easier to find pedigrees -- Bethlehem, say -- don't seem to bring much of a premium on more common or less desirable books. I've bought copies of such books where the seller didn't even note (or maybe didn't notice) the pedigree. There was someone a while ago arguing that pedigrees don't matter except for the top three or four (Church, Okajima, SF), but I would disagree with that.
Thanks everyone for your feedback regarding pedigrees. It helps answer my question and confirms what I was thinking.