With sugars what you want to think about is the fact that brown sugar already has a light scent. The brown sugar compliments fragrances like OMH but doesn't smell so great when combined with scents like Lavender,etc. Many people use sugar in the raw for scrubs, Not sure why, I have not looked into it. many sugars are filtered through bone marrow, therefore they will pick up & contain minute fragments of bone. That is something to consider if you are planning to make a vegan claim.
With salt one main issue to consider is how much you think you can retail your product for. Dead Sea is considerably higher in price. You may think about a blend, maybe 20/80, etc.