I'm fine with cooking in the winter, because I heat the house anyway, and who wants to eat cold food in a drafty 63 degF house in the winter? It costs about a penny to reheat something in the microwave, so I'm not too worried about that. In the summer, though, we definitely cook less.
As for the health side, I think if the ingredients are healthy, and no deep-fat-frying occurs, the end product will also be healthy.
For sure, though, recipes with no cooking often take less time to make, unless there's a lot of chopping involved.
Using a slow-cooker or pressure-cooker instead of a range top or oven saves you a ton of energy.
A slow cooker is a great tool, and we use it all the time to make soups, Greek yogurt, etc., but I think it's less energy efficient than stove-top cooking.
Any ideas for a no-cook breakfast in summertime? Right now, we often eat homemade granola (requires pre-cooking), oatmeal, eggs, and/or pancakes, which all require cooking. I guess LMGTFmyself...
Cold oatmeal
http://www.katheats.com/?page_id=3889