I have noticed the same problem... the shoes seem to lose their "gumminess" after a while. Currently I have been keeping my racing shoes in a sail bag after I let them air dry... and they seem to still be effective after about 2 years. I tend to go barefoot on my own boat (and no, I don't stub toes)

The problem is the shoes have to be completely dry before storing them, otherwise they will get quite funky in the closed bag.

It would be nice if there was something that could be applied to the bottom of the shoes to "revitalize" them.