Rook, nice post!
I agree though both internal arts in nature bagua is much different the aikido. thoug I have heard many times that Usheba was influenced by bagua and studied in Manchuria, I wonder about this. I have heard of many founders of non chinese arts going to China and learning various arts, it is possible, but when you research how the Chinese feel about outsiders and how they taught publicly in those days, you realize the odds of them passing any real information on was highly unlikely. even today we see the closed door students, especially in the internal arts, they are taught much differently then the avergae student or what is often termed as public teaching.
all internal arts use whole body, constant motion, and 'soft" force ( bad wording but hard to describe).
Bagua's spiraling moves are unique, every move is based on a spiral motion, making the throw in application much different from aikido. bagua's stepping is unique to all other arts, and derives from the use of spiraling energy.
bagua forms can be linear, but most often are circular based, usually begiining with a larger circle, and palm changes performed upon the circle. qigong can use static posture on the circle. later the circle changes to many smaller circles, some 8 stp, some 3 step and various ones as well, this is do the constant change of bagua. at the advance stages free form becomes the main solo training, this is where the endless change occurs and a form can last litterally for hours.
baguazhang translates as eight trigram palm, palm is emphasised do to the extensive use of the open palm. there are also other styles that incorporate the palm, even some tai chi forms, atleast one i have heard of, uses only the palm and juijitsu also uses the palm more than the close hand.