Excellent summary, you are 100% correct. Farm produce should be monitored for nutritional quality. The results should then get factored into the price. Instead of only using weight, they could use Weight x 'Nutritional Score.'
The scores should then be made public on the packaging so people have the choice of purchasing the cheaper 'lower grade' produce or paying a premium for the top class stuff.
This would incentivize farmers to focus on quality as much as quantity as both factors would influence the price equally.
Governments could then also set a minimum nutritional standard in all foods.