Obviously it depends on the level of crime where you're parking. I would consider a nutted wheel adequate security for the wheel, (I would u-lock the frame and not worry about the wheel, but I would not u-lock the wheel and not worry about the frame). The only things I've ever had stolen off my bike were accessories that did not require tools to remove.
I don't see that it's any higher security to throw a cable through your wheel. In either case, a tool is required to make the theft, but nothing that is uncommon or can't be easily carried around and concealed when not in use. Both is obviously higher security, since then you'd need two different tools to carry out the theft.