[Big up-front disclaimer - this is amateurish, random & composed of wild speculation. Take this seriously at your own risk. That said, I'll try to clarify my reasoning where I can, so you can form your own conclusions.]
Tim Powers is the author of thirteen novels and countless chapbooks. He's a persistant award-winner and nominee, as well as a literary favorite. Powers is the sort of genre author that other genre authors frequently cite as a favorite. He writes detailed, deliberately-bizarre alternate histories.
The book I'm going to single out as the one with the most collectible potential is On Stranger Tides.
First published in 1987, this is an enjoyable romp featuring pirates & the search for the fountain of youth. After the jump, three reasons why this book is my pick as a collectible prize.
1) Disney. On Stranger Tides has been purchased by Disney as the core story of Pirates of the Caribbean 4 (released in May 2011). Can you imagine a better tie-in for brand awareness? This book will be everywhere, with a little "inspiration for..." sticker on it.
2) Mass market appeal. Powers is a brilliant, complex, intellectual writer. On Stranger Tides may be his most accessible novel - straightforward, fun and action-packed - it could even work for a young adult market (see above). A mass market boost for the Powers brand should lead people to this book. If you'll forgive the comparison, On Stranger Tides is to The Anubis Gates as The Scar is to Perdido Street Station. The latter possesses more literary excellence, the former is more popular. (Please, please forgive the sweeping generalizations. I kind of hate myself for them already.)
3) Sub-genre appeal. On Stranger Tides is, depending on how one defines the term (nobody can), steampunk. Victorian magic, pirates, zombies, lovely outfits, a bit of romance and some big ships... there's a huge, existing, obsessive fanbase just waiting to notice this book.
Powers, in general, is a tipping-point sort of author. He's won awards, indisputably been brilliant and is an oft-cited name when it comes to favorites and influences. One little nudge is all it would take to push his books over the edge into collector's items. The gamble, of course, is whether or not the Disney movie is enough to do this. I'm betting it is - and not just as a short term boost, but, after an initial spike in interest, the book is good enough (and appealing to enough audiences) to keep its legs.
Also worth noting, that On Stranger Tides has, by Powers standards, not been frequently reprinted, with an ultra-expensive edition from Ultramarine and a limited from Subterranean. The first edition (hardcover, Ace, 1987) was the first time Powers had a commercial, first edition, hardback release - further adding to its appeal to collectors. It is rare, but still hovering in the $50 - $100 range (barely more than the Subterranean edition). I can't see how that can hold.
Conclusion: On Stranger Tides should be the iconic title of an author that's poised to move from a cult hero to mainstream success.