I am an atheist!
And though I don't agree with (most of) his ideas, so was the philosopher Friedrich Nietzsche. And HE believed in a SOUL. A soul is the innermost constitution of your being. Its existence does NOT require the existence of a god or other such fantastical entity. When you say, "That little rascal has SPIRIT" that "spirit" that you refer to... that is what I call a SOUL. So, yes, Data has a spirit, a soul. IMHO.