Once a novel gets going and I know it is viable, I don't then worry about plot or themes. These things will come in almost automatically because the characters are now pulling the story.
We don't need a melting pot in this country, folks. We need a salad bowl. In a salad bowl, you put in the different things. You want the vegetables - the lettuce, the cucumbers, the onions, the green peppers - to maintain their identity. You appreciate differences.