This is an interesting question. It's related, in a way, to a famous objection to Descartes's "I think, therefore I am". The objection was: What's with the I? Why not just: Some thinking is happening? So maybe the dog can be thinking: Petting would be good. Eating is good. Baths are bad! Frisbee is good! Etc, etc.
Another important point to make is that one doesn't have to think that dogs have the same worth or dignity as human beings to think they have worth and dignity, even that they have quite a lot of worth and dignity. Personally, I'm more of a cat person, and, whether or not my cats are self-conscious, they are sophisticated social beings, with each of whom I have a complex, individual, and mutual relationship. There are no doubt limits to their mental capacities. But there are limits to our mental capacities, too. And I think it would definitely go too far to say that they have no appreciation at all of the difference between minded and unminded things. There are lots of things they do that suggest rather strongly to me that they have some understanding of that distinction.