I don't remember where I got my first Lunaria plant or seeds. I do know, however, that over the years it's become a pest with new seedling popping up all over my 100 x 150 ft lot here in Montgomery, AL. As I've worked my beds this spring and early summer, I've systematically pulled up at least 95% of the plants and even more than that of the ones that have already set seed.
Yes, the blooms are attractive and add color at a time when not much else is blooming. However, enough is enough! It will be very limited from now on.
I do understand your feeling about the prolific seedlings and I pull many as I work around the yard, and eliminate some of the puny ones. I really don't feel plants to be invasive however unless they are hard to pull or eliminate. Over enthusiasm I can take!.