The big issue with atheist spirituality has nothing to do with the aesthetics, but rather has everything to do with the underlying meaning. Frankly, atheists can feel wonder, joy, and etc, without a deity.
There is an issue of why isn't an atheist going to be, at a methodological level, a nietzscheite nihilist? There is no reason why atheists are going to be nietzscheite at a practical level, this world fills you with good feelings as it does with most people, but why NOT egoism? I would even argue that there is an issue of why theists aren't nietzscheite nihilists as well that they need to try to grapple. After all, the existence of the ego is plainly apparent, as is its importance, as this "oneness" that you feel is not a consciousness and you clearly exercise your will in your life and activities and well, to be honest, every single thing you do is related to the self, so why not Nietzsche? Or to be more precise, Stirner?
"God and mankind have concerned themselves for
nothing, for nothing but themselves. Let me then
likewise concern myself for myself, who am equally
with God the nothing of all others, who am my all,
who am the only one.*" -Max Stirner