The word spiritual is a loaded term, isn't it?
Among other things, it can mean non-physical, supernatural, and sacred. Aikido doesn't seem to me to be exactly any of those terms.
Words I might use that come to mind regarding Aikido are, in my opinion: connecting, relaxing, calming, respecting, etc.
Maybe it is the shift from competition to cooperation which is important in Aikido.
It was important for the country of Japan and perhaps for any of us who desire simplification in the face of some kind of struggle in our lives.