I don't like kale, but we do eat spinach. As long as it's still got
some crispness to it, I would tear off the bad bits and use it in a cooked dish, but not something like a salad. If it was wilted completely, I'd throw it in the compost. Try tearing off the bad bits and giving it a soak in some cold water. That crisps up garden lettuce if you've harvested it in the middle of the afternoon when it's hot, which wilts it somewhat.
How are you storing your veggies? They each have different needs for storage (humidity, temp, etc.).