Here is my problem with the excuse that the rattles are due to economic reasons.
Having worked in dealership service departments for Infiniti, I know from experience that the vast majority of rattles can be fixed with a few pennies worth of padded double sided tape placed between the parts that rattle.
Now, as you go through pre-preduction testing you identify the parts most likely to cause rattles. You then apply the padded tape as part of the manufacturing process. Total cost would be pennies in materials and perhaps as much as $40 in additional labor.
So, you increase the price by a mere $50. The rattles are eliminated and Ford actually makes MORE profit per vehicle.
I find it extremely doubtful that anyone interested in buying a Mustang is going to change their minds if the car costs just $50 more than it does now. It would still be competitively priced with other cars in it's class.
So sales would basically be the same, profits would be increased, and customer satisfaction would be higher. Higher customer satisfaction coule even lead to an increase in sales which would increase revenue and profits even more.
Ford just can't be bothered because their bean counters in charge simply don't care. They all drive Mercs and Lexus, and don't care about Ford interiors.
I bet if you required Ford execs drive Mustangs exclusively you would see a very different interior in the car.