I'm...going to do what ought to be done with them: I'm going to read them.
(I also picked up an edition that collects Merritt's other two novels in one book for fifty-eight cents. It's been good hunting lately.)
First up: The Face in the Abyss, A. Merritt
There is a particular kind of disappointment that happens when you read a "classic" of Golden Age pulp fantasy and it's a total train wreck that leaves you thinking that maybe these books were only considered classics because of the limited options available at the time.
This is not a book that will give you that feeling.
Instead, The Face in the Abyss is the platonic ideal of pulpiness: it's got a hidden city with ancient white people ruling over dusky natives (!!!), gladiator fights with dinosaurs, a snake woman with terrible magic-science weapons, a villain who strikes me as a mix between Sauron and Skeletor, an attractive and frequently-imperiled heroine, and a square-jawed hero who reminds himself that he went to the Harvard School of Mines (!!!) during a moment of self-doubt.
So, yeah, this is not particularly forward-thinking stuff, but it's a ripping yarn. Nevertheless, for this sort of novel it does hold forth some surprisingly deft meditations on cultural degeneration. The conclusion needs some pew-pew raygun and explosion sound effects playing in the ground for maximum enjoyment, but that's left to the reader to supply.