Have you checked out puppy prices lately? They are really going down fast, and even breeders who have spent a fortune for special breeding dogs are limiting their litters because of the poor economy. While dog prices have gone down, vet prices continue to rise, and unless your financially solvent with a padded savings, I don't think I would risk it. You were really lucky with your first litter, and nothing went wrong, however, this doesn't mean it will happen again, and pregnancy does take a toll on mama, and especially her teeth. If I were you, I would do some research on the matter, there are so many different things to be aware of when you are breeding domesticated animals, it's not the same as if they were in the wild, once man steps in, man is often needed to continue to step-in to insure a healthy litter. The link has some good information.
Breeding Your Dog