Re: How spiritual?
IMHO, spirituality is a completely separate consideration from any physical reality. I believe that it's something which can only be experienced through literal spiritual practice, so learning spirituality through Aikido practice would be like trying to learn to box at a ballet studio.
In my case, spiritual practice led me to Aikido, as I was formerly learning some highly violent MA. I think if you're inspired by the non violence of Aikido, it could lead you to some separate spiritual study. I bet Ted Ehara could give you some better clues than I could, being a Ki Society brother.
I've noticed that Aikido draws very spiritual people and that is probably what makes it so easily confused with spiritual practice. You even hear a lot of spiritual talk around Aikido circles, but talk is just talk and practice is practice. Or as Alan Watts said, "You can't get wet from the word water."