Yes, but I don't think you should take it to its logical conclusion

I'm just saying it is a useful way to sort out garbage...when there are many books with proven value, and another book has dubious value, then it helps you filter to some extent the books you read. It is risky to read something of unproven value.

Value can be defined several ways of course, giving Timothy Zahn value because he is very entertaining (usually).

In the case of The Shack, the common argument for reading it is that it "gives you a unique perspective on God" or something like that. It helps you understand God better, etc. Now if the purpose was just to entertain yourself, then you don't necessarily have to worry about finding the absolute most entertaining book in the entire world. A book of decent entertainment will do. Of course, when we find one that is especially entertaining, we of course share it. And my siblings cannot deny that I have shared many entertaining science fiction novels with them (from Midshipman's Hope to Hyperion, and beyond).

But when the "value" ascribed to a book is spiritual, and especially when the book is meant to be a "picture of God" or whatever, then perhaps we ought to be more careful. The value of the Shack being unproven, the amount of books with proven value (defined in spiritual terms) being prohibitively high, leads us towards other books.