I'm with you on the virtue of agnosticism. It is more honest than atheism.
I disagree with you though, if I'm reading it right, that the spiritual has to be contained in reality the way it is. I think there are myriad false assumptions loaded into that statement, including that reality is only what we can sense with our physical sensors, or that the physical world is the majority part of our existence. We have an additional sense that we sometimes call intuition that tells us there's more to existence than the material. That sense is grounded in the pineal gland, which is what helps us sense God. There's plenty of reading on that.
Agnosticism, in my view, is merely a starting point on a longer journey, which can lead to a wider awareness of what is (think Plato's cave). But when it is a state of being, it is an indicator that there's a problem with that humans soul that actually might start in the brain.