Those power plants wouldn't have been allowed to be built... so yes? With the modern regulatory environment, those three nuclear power plants would never have melted down (because they wouldn't exist).
Molten salt reactors might provide superior safety (the thorium is irrelevant to that). However, they also would likely imply higher operating costs, because now instead of being sealed in fuel elements your fuel is flowing through a larger part of your reactor, and volatile fission products are escaping into the off gas and have to be trapped in another system (which will have to be cooled to prevent melting). So you now have complex systems that are too radioactive for anyone to touch for maintenance. Reactor structural elements are also now exposed to more neutron radiation as well.
