My understanding of Spong's claim that God is the "Ground of all being" is that we are all created in the image of God and that we all have the capacity of God. The Hebrew term "tselem" fits here. It is kind of like the "Maker's mark" on Creation. (Sorry, I know all of the capital letters aren't necessary. Force of habit.) This doesn't mean that God exists in a pantheon only that God is reflected in Creation. This is also a Buddhist concept. I hiked the Kumano Kodo pilgrimage trail in Japan and there were sort of mini-shrines called "oji" all along the way. The Shinto understanding of these shrines was that there were different kami in residence at each shrine and that each one sort of embodied the surrounding of the shrine. The Buddhist understanding of the same shrines was that each one represented a different instantiation of Buddha. I think Spong's understanding of God reflects the latter.

In answer to your question: I think that we can have an intimation of God. We cannot "know" God perfectly and a lot of theological problems arise when too many labels are applied to God. It's problematic to say anything about God at all. I am an anomaly in the Christian community as is Spong. I don't think there is much that can be said about God and I make very few claims about the Divine. I don't say anything that I don't think I can back up and I never cite scripture as evidence. I would agree that many people need to change their understanding of God, because, frankly, most peoples beliefs about God are theologically shaky. But I don't think that attaching more or different labels is the solution. I just think that more people need to be comfortable saying "I don't know" instead of scrambling for a bad response to questions that we just can't always answer. Is that fair to say?