Aikido spirituality is important because the spirit individuals bring to the practice mat is the essence of the community of that dojo. The physical challenge of training is exhausting and exhilarating at the same time. But without the community, it's really no different that joining a swim club, or training with a group to run a marathon. When I train at a dojo, I trust each person I practice with to refrain from hurting me. Whether they treat me with compassion or with callousness is a reflection of their spirit, which in turn is a fruit of their spirituality. The further along in life I get, the more I realize just how precious are the friends whom you can trust with life and limb.
I am a committed follower of Jesus, and it has been my choice to thus define my life for the past 25 years. So the spiritual impact of where I choose to invest my time, my relational-coin, as it were, is significant to me. I find in my practice of Aikido, a physical echo of my desire to love each person God puts in my path. To accept each where they are and redirect the energy they give me in a positive direction (towards healing and reconciliation with God). And to really have that ki-ful smoothness, you have to not only understand what it is that you are trying to do, but also be deeply aware of what uke is doing. Aikido helps me understand compassion, gentleness.
And when I get too full of myself (oh, about every 15 min or so, maybe less) I get a good practical lesson in humility!