Oh no, not at all, as regards Tolkien. For example, a while ago I read at last
Athrabeth Finrod ah Andreth in the History of Middle-earth volume called
Morgoth's Ring. I will say only that it is important indeed for Tolkien's conception of the destinies of Elves and Men; intellectually stimulating; and moving. It is a major work, although not one for people new to Tolkien. Or take the long portion of
Sauron Defeated that is given over to Tolkien's unfinished novel
The Notion Club Papers, which I would say begins as an occasionally satirical fictional symposium and develops into the closest thing Tolkien ever wrote to a Lovecraft novel. If you like Tolkien and you like "The Shadow Out of Time," hasten to get hold of this remarkable work.
After you've become acquainted with
Notion Club, check out the blog on it written by Dr. Bruce Charlton, Reader in Evolutionary Psychiatry at Newcastle University. He's been squeezing interesting things out of the
Papers for several years.
http://notionclubpapers.blogspot.com/
My feelings towards Christopher Tolkien are gratitude for making these things available and admiration for his searching and uniquely insightful scholarship. Thanks to Christopher and his publishers, one doesn't have to travel to Oxford or Marquette to review Tolkien's manuscripts. A guy like me in rural North Dakota can explore the development of Tolkien's images and ideas without ever leaving home.
Publisher cupidity? Hardly -- given that one or two of the posthumous books haven't even been picked up by Tolkien's American publisher. At least, so far as I know the critical edition of the "On Fairy-Stories" essay (ed. Flieger and Anderson) was not published here. It contains some nuggets I was very glad to get hold of, such as Tolkien on M. R. James's
Ghost Stories of an Antiquary and J. M. Barrie's play
Mary Rose (which was revived here in the US a few years ago, btw).
I admit I'm behind in my Tolkien reading and haven't read the two recent books, the Sigurd and Gudrun and the Fall of Arthur fragments. I'm thankful to have them.
I do think it would be nice to have a sort of thick "Best of" the
History of Middle-earth and other posthumous books. Much in these books is indeed for the Tolkienist, but there are fans of LOTR etc. who would like some of the items found in their pages, suitably introduced.