Additionally, it seems unclear whether the Peace Prize is primarily meant to reward or to encourage efforts toward global... let's say "altruism", since "peace" seems too narrow.

Perhaps the peace prize is primarily meant to maximise the use of the word 'Nobel'. Ambiguous wording is perfect for achieving that goal. It allows the prize to maintain the credibility it borrows from the Nobel science awards while also promoting controversy. An ideal execution of posthumous PR strategy (assuming getting crucified while founding a religion is out of the question).