Why limit these cards to only 3 of each? Players are already limited to only 3 cards per scene and cannot play a duplicate card when facing a Challenge, so why not allow Strengths & Weaknesses to be unlimited?

The Strengths & Weaknesses you begin with are the core concept of your character, so why not make it possible to always use them? You then wouldn't need to refresh cards in the current way and could instead have the option to add a new Strength or Weakness upon playing your last Sub-plot card. The total variety of Strengths & Weakness could still be limited to three of each, allowing you to expand the range of your character without diluting their core concept.