In The Antichrist, Nietzsche says that Christianity and Buddhism are both religions of decadence. What does this mean? Specifically, what are the hallmarks of such a religion? What are its values? What does it say about the culture in which such a religion originates or thrives? What does it say about the psychological state of its adherents?
I feel that the Western world was very muddled about Buddhism prior to the 20th century and often still is, but that these days, especially with the internet, it is much easier to see what is really is. The crucial point may be that Buddhist philosophy is not a speculative venture into the unknown but an attempt to describe the facts. It is a pursuit of truth and not the promotion of an arbitrary set of values or a mere cultural phenomenon. This would be why I do not like the implications contained in the question. Cold-hearted metaphysical analysis endorses the conceptual emptiness that results from a reduction of existence, as Kant shows, so we don't have to be in any particular psychological state to conclude that Buddhist philosophy is at least more or less correct, just as Nagarjuna famously demonstrates.
Also, many people argue that Buddhism is not a religion, which complicates things. I believe it is a religion but equally a science, a philosophy and an art, and this is a common view.
Nietzsche has a lot of interesting thoughts but (imho) is unreliable on both Christianity and Buddhism. Had he been alive today I'm sure he would have written differently. The questions about values, cultural background and state-of-mind of Buddhists are interesting and worthwhile but I feel they'd best be answered without reference to Nietzsche. Best to just ask a few Buddhists. Buddhism thrives all over the planet so the chances are that many Buddhists share your cultural background.
I have no idea how he arrives at the idea that Buddhism is a 'religion of decadence' and it suggest a lack of familiarity. I imagine that when he calls Christianity decadent he is referring to the sort of Christianity that is wildly inconsistent with Buddhist teachings, not the form of it that would be consistent, so lumping them together indicates a misunderstanding.
But... I have the impression that his complaints about Christianity were not wide of the mark, and that he would have been much happier with the form of it that is consistent with Middle Way Buddhism and Zen. This was almost unknown in his time thanks to centuries of efforts by the Church (both Christianity and Islam) to eliminate it. We must thank the internet for making these efforts pointless in modern times and for allowing us all to investigate where, when and how European Christianity developed all the faults he and another ten thousand other philosophers including me criticise. These criticisms largely evaporate for the classical and original form of the religion.
A rather waffly answer I'm afraid, but maybe it contributes something.
Cuvier says that "life is a vortex that pursues a constant path". It's always taking in matter, maintaining its metabolic life. Nietzsche speaks of a stunted tree on a stone, high in the mountains, its roots constantly seeking sustenance. Growth or death, passionate expansion or pitiable decline. In contrast to this, the spirit of the religions you name, tend towards Nirvana or cosmic extinction, the desire for equality, ultimately, Nietzsche identifies with the deadliest essence of a decadent being, and the inorganic privation of struggle. In a certain sense, this idea can be given in the slogan, nature is aristocratic; so that the convex side of this concave statement shows up as the unnatural, the stunted, the spiritual, Buddhist longing for non-being, & the modern secularized Christian Democracy, as sterile as septic liquids. It is the contrast of Geist: the true and the theoretical world (Buddhism, Todestrieb, Cybernetics, not to be troubled, but to be reassured, Christianity, Philosophy, Scientism), and, on the other hand: the unconstrained "Yes" to "Life".