Today, when you accept an answer you did not provide, you get a +2 reputation, however, if you accept your own answer, you get +0.
I expect the reason for this is to stop people gaming the system by asking and answering their own questions repeatedly.
However, this has the downside of providing a disincentive of accepting your own answer when it seems the best and instead accepting an inferior one in order to get the reputation bonus.
Therefore, I propose that the accept your own answer is only worth zero when there are no answers provided by anyone other than yourself.
I feel this keeps the intent of preventing gaming the system for reputation, while removing disincentive from picking the best answer, even if it is your own.