The re-sale value of your car won't be much affected by aftermarket parts. I mean if carvana offers you X amount of dollars for your car, they are not going to compensate you accordingly for all the extra bolt on parts you may have added. They might for one or two specific items but I think as a whole they won't ask. I think most people (and I agree 100%) find that selling the parts individually is much more profitable than just "giving them away" on the car....