You do realize that's because they are cheating the event to make it that way, right? The princess in third place gets 3x the points, the princess in second gets 2x. So even if someone gets one princess 100,000 points by spending $1000, the others will catch up within a day or two.
It is absolutely pointless to worry about helping your princess right now, because no matter what you do, your efforts are meaningless until the last hour or two of the event.
- - - Updated - - -
Story missions give a 1:1 ratio of stamina:exp, so just do those if you want to level up. It will happen over time though!