Hi Mike,
I think for the main bulk of your question you might be better off in the Modo forum! 
Why RC crashes when you use the external unwrap can be caused by many factors, I’m afraid I can’t help you there.
But the reason why RCs textures are worse on the simplified model is probably caused by the difference in geometry from the original mesh to the plain surfaces you created. If you imagine a wavy surface being projected from several directions (individual images) onto a flat surface, there are bound to be errors. It very likely is caused by the fact that the reprojections end up on a different spot from each image, so that is seems blurry when all are combined (which is what RC does). You will probably really need to use external tools for selective reprojections to get the results you need.