Regarding #65 and #66, I was considering opening my practice about 30 minutes away in a town called paradise california. it's a mountain/retirement community, if I were there I'd have picked this logo in a second! It's a great feel. I'm sorry to say though that the feel doesn't match my current town.
In the general comments I've provided two links with a positive and a negative example of a tree. The oak tree is the unofficial tree of Chico, CA (where I practice) and I think a silhouette of one would be very good inside the circle of #64, or standing alone in #63.
Or maybe a bonsai tree.
Finally, the sacrum, or the last bone at the bottom of the spine, is a little too weak looking in these spines. Some thing more symetrical or less curved would help.