To me the vitamin content in organic food is not the main reason I choose to buy organic food. I think pesticide residue is a bigger issue. While organic foods also use pesticides, they also try other options for pest control. The pesticide issue is not just an issue for the consumer but also for the farm workers. Organic foods are not allowed to be GM, so I would argue they are healthier since this means organic foods are not genetically modified (and not possibly tumor causing). This is true for conventional foods too, but sometimes it is hard to decipher between conventional and GM since GM companies like to hide the fact that their products are GM.
The fact that GM foods can cause tumors in rats does not surprise me at all. This is why so many people have been fighting for labeling on GM foods, not because they knew there was something wrong but because there was a big unknown with these foods. Many of them have not been tested long term to know the health impacts they might have, but now we are starting to better understand these foods with some long term studies. Hopefully this gets a push toward better GM labeling on foods and to have the press stop bashing organic foods.