From my understanding, he certainly received high accolades from many of the literary lions of the time, including Ambrose Bierce, Vincent Starrett, George Sterling, etc. But, unfortunately for Smith, he was very much a traditionalist at the very time when vers libre and its congeners were becoming all the rage, and soon his work fell by the wayside in literary circles. He may not have been the best living American poet of the time, but his work certainly deserves to be high up there. He had his less successful poems, but the vast majority of his work is really exceptionally powerful and rich -- it is definitely the sort of poetry one compares to a truly fine wine; heady stuff, and well worth reading. I posted his poem "Medusa" on the thread dealing with Alphabetical SFF, under Gorgons, following a discussion of Medusa and Megaera with Chris. Give it a whirl and see what you think. There's also a site called Eldritch Dark, devoted to CAS, and some of his poetry -- as well as a great deal of his artwork and some of his prose -- is posted there.
As to Joshi's book, it's recently been reprinted by Wildside Press, I believe, and is pretty reasonably priced. In it, he has rather substantial examinations of Machen, Dunsany, Blackwood, Bierce, and Lovecraft, plus a shorter chapter on M. R. James, whom he had the courage to rather take to task for leading the ghost story into a very small alley. Then there's his The Evolution of the Weird Tale, which covers W. C. Morrow, Robert W. Chambers, F. Marion Crawford, Edward Lucas White (he has apparently put together a book of E. L. White's best weird work, which hasn't seen print for a very long time, except for "Lukundoo"), Sir Arthur Quiller-Couch, Rudyard Kipling, E. F. Benson, L. P. Hartley, HPL (different from the chapter in The Weird Tale), Frank Belknap Long, Rod Serling, L. P. Davies, Les Daniels, Dennis Etchison, David J. Schow and Poppy Z. Brite (the last two he sees as somewhat interesting and talented, but tending to be too hackneyed at times). And The Modern Weird Tale, covering William Peter Blatty, Stephen King, T. E. D. Klein, Clive Barker, Ramsey Campbell, Robert Bloch, Thomas Harris, Bret Easton Ellis, Thomas Tryon (if you've not read his The Other or Harvest Home, read them before reading this chapter), Peter Straub, Robert Aickman, Anne Rice and Thomas Ligotti. Each has bibliographies of the authors' works, as well (often extensive). As always, very valuable reference guides, and thoughtful (and thought-provoking) criticism here. One may not always agree with S. T., but the man certainly commands respect.