Wannabe, I don't know if it alters the nutrition. It may, because if you are breaking down the tough cellulose(?) walls, it may release some vitamins. However, I found this on Web MD:
Beyond antioxidants, the fiber content of cruciferous kale binds bile acids and helps lower blood cholesterol levels and reduce the risk of heart disease, especially when kale is cooked instead of raw.
So if some of kale's benefits are enhanced by cooking, perhaps they are enhanced by marination as well? Usually I think of cooking a veggie as reducing its health benefits. Ah, that kale -- it never ceases to amaze!
Here are some kale salad recipes I found:
kale salad recipes
When I make it at home, I usually do a dressing of cider vinegar, olive oil, garlic, salt and pepper. I throw on sunflower seeds as well. Or a white wine vinegar, sesame oil, and soy sauce dressing. Sesame oil has such a strong flavor, you don't need much!
The massaging is important. You rub the dressing into each leaf, front and back. Cooks Illustrated did a side-by-side test and it really makes a difference.