Theoretically, organic products are healthier than non-organic because there is a reduction in the introduction of foreign chemicals/carcinogens into the body---things like growth hormones from cows, pesticides, etc. Organic products are also supposed to be better for the environment. I often get questions regarding the value of something being "organic."
I think it's important to assess what the organic label actually means on a case-by-case basis. Let's use organic milk as an example.
Research has shown that organic milk is higher in omega-3 fatty acids (by an average of 68%)--but this would not be the case in fat-free milk due to it being fat free. There are other benefits/nutrients in the milk from cows that have been free-range-grass-fed, especially if they ate clover (which is higher in cows raised for organic milk).
The problem with organic milk is that even though the cows were fed organic feed (which is better for the environment and does not contribute to passing pesticides onto humans), they are still usually just factory farmed cows, with minimal field-time. In addition, organic milk farms are less prevalent, and so the product has to travel further to get to the consumer. This means it is often the same or more processed (heated to a higher temperature) than regular homogenized milk. Some people find that their organic milk lasts longer in the fridge than regular milk, and other people find the opposite.
I think the bottom line is that buying organic fat-free milk would just cost you more, and there could be a minimal health (but no real environmental) benefit. The Natural Health experts would say the best thing to do would be to find a certified raw milk producer locally (and make sure its clean and reputable), then you've minimized the health and environmental issues associated with both homogenized and organic milk. However, you wouldn't find fat-free milk that way! So that was a really long way to say-----personally, I wouldn't pay for the tiny benefit, but those who are passionate about it say its worth it. That being said, I may feel totally differently about organic grapes.