I hadn't heard about poly filling dulling my pins! Isn't great how much we learn from each other without even trying? I have heard that steel wool is also good for keeping pins sharp too.
You know the old fashioned "tomato & strawberry" pin cushions? The "strawberry" is also to help keep your pins & needles clean & sharp. You put your pin or needle into the strawberry & squeeze the 'berry' while spinning the pin. That one I saw on Eleanor Burns. :D