Clues and they way they are "dropped" into mysteries can intrigue a reader, confound them, confuse them or challenge them. The lack of clues can anger a reader. It is no fun to have a twist or solution dropped on you at the end of a book or story with no prior indication. Do you believe the reader deserves some valid clues to solve the mystery, even if it was a very subtle clue buried in prose at the beginning of the book?
One mystery I read recently (Murder on Safari, by Elspeth Huxley) tossed in, at the denouement, page citations of each clue used in the solution. This deals with a problem that could (maybe) arise at times, in which a reader might say, "well, I don't recall anything like that being shown!" I'm not sure how difficult inserting those references was for the author and publisher, but it seems like a useful idea to me.
Oh, I love that idea - coming from a reader's viewpoint.