Yes, but the cures here aren't general. They're highly specific, and the rare conditions have a long tail- large numbers of different conditions, each with a very small population of affected individuals, and likely, the treatments will be somewhat customized for each type of disease.
See my comment above. Getting approval for rare diseases and expanding the indication to the common form of the disease is a well established strategy in pharma.
yes, but that's totally different from coming up with a generalized treatment for a wide range of "rare" diseases.