30 million people in the US are affected by "rare" genetic conditions.
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.
Also rare genetic diseases give insight into the underlying mechanisms and pathology of common sporadic diseases, which can be leveraged to develop new and better therapies.
Getting a new drug or therapy approved for a rare form of a disease and then expanding the indication to the common disease patient population is a well established strategy.