I'm not up for seeing a change in this. While I don't particularly trust vouches, I do consider them when trading with people, or deciding to help people. I like to know what others think of someone, I like to get to know the person I'm trading with. If someone vouches themselves, then I can't be sure who I'm trading with, I can't know exactly what others think of them.
And there's only one intent behind self-vouching, and that's the furthering of oneself. A greedy, and selfish act that should be punished irregardless.
A case by case basis, I believe, is acceptable, but the rules and grounds for punishment should not be changed simply for this. The rule remains the same, exceptions are permitted. It's no question that this whole thing is coming up because of Nate's contributions, but I really do believe that you have to consider his self-vouch before all of his other contributions.
What if all his fantastic contributions to the site are in conjuncture with his self-vouch? What if he is just trying to get to the point where he's trusted with enough people that he can freely scam without much scrutiny or suspicion? What if all the other people who have been banned would have contributed the same as Nate, or more?
These rules protect buyers and the website as a whole. While less strict punishments may be appropriate on a case by case basis, there is no doubt in my mind that the normal punishment should remain a permanent ban.
When it comes down to it, however, I support a 3 month ban, permanent market ban, and a very lengthy TWC... for exceptions only.