I think it provides incentive to not be a part of the bizarrely hated Bush administration. Since he's unlikely to be president again, it won't have any effect at all.
The more it happens, the more powerful it will become. Imagine Google appointed James Clapper to their board. Don't you think there would be a response?
It would only be news if was consistent and applied to everyone. Microsoft, Apple, Google, Yahoo, etc all supported Obama, and the things he's done with the NSA are at least as bad as what Rice did. Dropbox and Rice are getting fallout because of some bizarre hatred for the Bush administration and not some newfound resolve to be ethical at all times. Yes Google would have fallout for appointing Clapper. They wouldn't have any from Hilary Clinton or Joe Biden or Obama himself, which would be the real equivalents to Dropbox appointing Rice. FWIW, Google also can't appoint Keith Alexander.
I agree with you that all of these people should have their political records examined when they join corporations. Supporting this action is a starting point to have this become a more widely used tool.