From this collection I've read:
3 Gustav Meyrink, Cardinal Napellus
8 Pedro Antonio de Alarcón, El Amigo de la Muerte
16 Jacques Cazotte, The Devil in Love
30 Argentinean Tales
I'm pretty sure that without Borges I'd never have heard of Cazotte, Alarcón and Meyrink, let alone read them. A trio of worthwhile classics.
My selection process was guided by my inability to find these stories in other formats/collections/volumes. If I want Henry James or Poe stories, I'll just go read their collection short fiction; same with most others. The volumes are indeed very short, nearly samples for the inexperienced, and there are better alternatives that give you more bang for your buck. Their value lies mostly in the awesome covers and in the lovely prologs Borges penned, veritable love letters to his favorite writers.
It's curious I found out this thread, I wasn't even looking for it. Today I actually started reading La Biblioteca de Babel (2000), a collection of the prologs and nowadays a hard-to-find book. Borges was first approached in the 1970s by an Italian editor, Franco Maria Ricci, to edit a collection of authors Borges loved. Between 1975 and 1985 33 volumes came out. Several countries - Spain, Argentina, Portugal, that I know of - have tried to reprint the whole series, with varying degrees of failure. Spain had the best run, with 30 volumes. Those are the prologs that compose the book I'm now reading. They were never reprinted again after 2000 and the volume has been long out of print. It's a shame because it shows Borges' love for fantasy (not magical realism) very clearly.