There are some that say the external ballast (or ignition) resistor protects the coil and I think the ballast resistor definitely protects the points, speaking from experience. I'm surprised the coil blew up just because you didn't have a ballast resistor...you may want to check your points. Is it possible you were running a 6V coil in a 12V system? That could mess the coil up good.

If I had to use points, I would favor the external ballast resistor set-up. That way, you replace only the component that is bad (coil or resistor).