I think that both the nihilism and the "joy in the merely real" come from a sort of subjective imagining and have very little connection to knowledge. The people for whom materialism threatens nihilism at first imagine themselves to be living in one sort of world; then, they imagine another sort of world, and they have those responses. Meanwhile, the self-identified materialists have been having their experiences while already imagining themselves to be living in a materialist world, so they don't see a problem.

Doesn't this support simplicio's thesis? If there's little connection to knowledge - which I take to mean that neither emotional response follows logically from the knowledge - then epistemic rationality is consistent with joy. And where epistemic rationality is not at stake, instrumental rationality favors a joyful response, if it is possible.