Hey Curt,
you asked what the best material is for shelves on bows. Since I haven't used all of them I can't comment on what is the best, but I personally use adhesive backed velcro for my bows. Cheap, easy, replaceable and, in my opinion, good looking, Yet, at the same time, it is not the most durable material out there.
You do make an interesting point about forgiveness. I would think a consistent, durable(doesn't wear down effecting nock point), reasonably dense yet not too hard material would be the ticket. I suppose too soft and wear would change nocking point, too hard and bad releases would not be compensated for. Thoughts?