If Jesus is the son of God with supernatural power the clay and spit paraphernalia are obviated, as has been pointed out to you repeatedly. It is not unreasonable to ask why they are used in this "miracle".
My thought would be to reference the creation of man from clay as described in Genesis two.
I personally don't think it would be odd to use props even though they aren't necessary to the performance of the miracle. There were observers and the props could have been to have an effect on them or to transmit a message to them.
Admittedly, it could also be because that's the way a magician's tricks would be described in that day and age. Since we weren't there, I don't suppose we'll ever know unless the resurrection is true and he or other eye-witnesses let us know.