May I insert a brainstorm?
What about you do the tornado in layers.
Layer one would be the bulk of the body done with the cloth sim. What I am thinking of is a tornado shaped cloth rotating at high speeds. Maybe you should tweak the local stiffness of the cloth to maintain that characteristic twister shape.
The next layer should be something like a thin cloud texture attached to the tornado (like in the realistic clouds in Max thread).
The last layer should be flying debris flying chaotically around the tornado. I think that this could be best done with boids because although the debris might be rotating around the twister, from a distance it looks like a swarm of mosquito’s.
Finally at the mound of the tornado, setup a emitter that spewing up fine dust.
About the cloth idea, maybe the twister should be rigged so that it won’t collapse on itself, Maybe some internal stiff edges?
The added advantage with this system is that you can make the twister make that ‘curvy dance’ using wind force fields.