Well, when the rubber starts to oxidize, as I'm sure your aware, they get a texture and they start getting brittle. While that might make them "hold scent" I think by that point you would be tossing them anyway. That's why I never leave mine out in the sun.

I always spray my boots down anyway before going in the woods.

Huntingson, never heard of burying them! I guess a couple days couldn't hurt. Do you roll around in the dirt/mud before going hunting? I know a guy who does that.