I've seen mixed dogs sell more than some purebreds because they are mixed with the favor of two breeds. I've seen Yorkie/Maltese or Morkies go for as much as $1500 because of the size, coloring and temperament. I don't think they are any less worth it than purebreds.
I have a purebred Mini Schnauzer that the breeder should not have bred, she is AKC registered and yet she's 20lbs!!! (I think one of her parents was a standard schnauzer). She's huge!! We got her fixed.
I have 2 male yorkie/maltese they are 3.5 and 3lbs fully grown, both parents are AKC registered. They are just as precious if not more than any purebreds I have or have seen. I don't think they are any less worthy just cause they don't have AKC papers...but then I am partial to them
My 2 cents on this is basically AKC registered doesn't mean they are superior to a dog that is mixed or doesn't have papers.