Hi Bob, glad to see you back and we're still thinking about you buddy!!
I guess the bottom line is you know that Henry did nothing on the Model-A here yet did so on the T's and early V8s. I guess it boils down to what are you trying to accomplish? In other words, what is the benefit? Personally I do not see any benefit of using leather/welting/grease IF everything is as originally spec-ed out. If the tie-bolt is correctly installed into the crossmember, along with the u-bolts correctly installed and tightened, the spring cannot move anyway. Also, the lower leaves are the moves that are moving the most whereas the upper spring that would be in contact with the crossmember hardly sees any deflection that would cause rubbing or a squeak. I guess my answer to you is decide what you are trying to accomplish and see if adding any of those helps you.