It seems the more we dispense with those third parties (payment processors, editors, courts etc), the more important personal reputation becomes.

I agree. I think that while there is the chance for centralized abuse, one of the things that blockchain will encourage is people who are consistently trustworthy and I reckon this is going to have some very large implications in the way things get managed in the future.

If I had to choose between losing all my SP, but keeping my name and reputation; or starting over fresh as a stranger but with the same SP, I'm not sure that'd be an easy decision.

That is a very interesting thought experiment. I think I would go with SP as I back myself to be able to build a reputation again :D