Rolls Royce used to lap each leaf together to obtain a perfect sliding surface which was then lubricated and covered with a leather gaiter to keep the grease in and the dirt out.
There is a modern alternative to place a Teflon type liner between each leaf to achieve the same effect.
There's no doubt that an unlubricated, dirty leaf spring will provide more damping and less springing but that's not what it's designed for.
I don't quite see how you can over- lubricate a leaf spring.
I grease mine and then wrap them in Denso tape.
