There are some authors whose books or published stories have a monetary value. Early authors such as Howard or Lovecraft or Clark Ashton Smith, especially in their old pulp magazine forms. And my interest is generally along the lines of authors who were the inspiration of D&D or AD&D or other RPGs. Authors both living and dead.
While I enjoy treasure hunting I don't collect authors for money. What I hunt down are their stories.
Tim powers would have been a pulp writer if He'd lived in the right era. His early novels would have translated well to Weird Tales. A combination of occult, adventure and historical madness. The Drawing of the Dark has a touch of the Illuminati Trilogy by Wilson & Shea, but is purely a tale of history and the remnants of mythology in the ever more modern world. The Anubis Gate and On Stranger Tides both have that touch of occult, history and adventure and all three have lively rounded characters both heroic and villainous.
I have been less impressed with his later novels, most dealing with modern twentieth, twenty-first century settings. Where he left a sense of mystery in his earlier work I found him explaining just too much in novels like Declare and Last Call. Instead of mystery I felt a bit dissatisfied with the endings, and a slowness of pace that made the thickness of the books a burden rather than a joy.
I will say that any of the Tim Powers novels I've come across have been worth the effort (except for Dinner at Deviants Palace, a science fiction set in the future, which seemed like a failed experiment rather than his normal craftsmanship).
Powers writes excellent stories. The early prints and small press items will be collectable in themselves in our more and more paperless world I do not doubt. They can easily be plundered for gaming inspiration (or movie scripts as I understand On Stranger Tides is to be ravaged for the 4th Pirates of Caribbean movie). I am glad to have Power's work on my bookshelves and gladly recommend them to any pulp reader or gamer who hasn't come across them yet.
Bibliography (edited from Wikipedia Entry)
^The Skies Discrowned (1976)
^An Epitaph in Rust (1976)
*The Drawing of the Dark (1979)
*The Anubis Gates (1983)
Dinner at Deviant's Palace (1985)
*On Stranger Tides (1987)
The Stress of Her Regard (1989)
Fault Lines series
Last Call (1992)
Expiration Date (1995)
^Earthquake Weather (1997)
^Powers of Two (2004) Skies Discrowned and Epitaph in Rust.
^Three Days to Never (2006)
Short story collections
^Night Moves and Other Stories (2000)
^On Pirates (as William Ashbless; written with James Blaylock) (2001)
^The Devils in the Details (with James Blaylock) (2003)
^Strange Itineraries: 2005,
Other published work
^The Complete Twelve Hours of the Night (1986)
^A Short Poem by William Ashbless (1987)
^The William Ashbless Memorial Cookbook (2002)
^The Bible Repairman (2005.
^Nine Sonnets by Francis Thomas Marrity (2006.
A Soul in a Bottle (2007)
^Three sonnets by Cheyenne Fleming (2007)