I first played AD&D back in 1980 but my gaming days ended years ago, so unlike many here I have no interest in Pathfinder. I do love the pulps however and looking up Planet Stories copies on Amazon has led me here.
Bringing back these lost or forgotten treasures is a great service and welcome treat but in my experience the core audience for these books are likely existing fans and/or collectors. Half of the lure will be presentation; I want an enduring, quality product that stands apart from my existing rag-tag collection of well worn, and typically paperback, copy. I know you're also trying to reach a new audience unfamiliar with many of these authors and in this you must succeed. Stories from more modern writers like Anthony should hook that target group and expose them to the brand thereby expanding the base.
Still, I have to believe existing fans will comprise your foundation and I can't see myself subscribing for softcover editions. I can just as easily pick off the issues I want from Amazon. However, if you offer me an exclusive hardcover variant, available only by subscription, then sign me up! I know I'm not the only fan and collector that would be willing to pay a premium for such an option. Have you done any market research in this direction?