What factors are used in determining a used car's value? Recent upgrades?

IMV is a program that calculates the worth based on year, make, model, mileage, and what other vehicles are selling at in that range in your location. So any upgrades and parts mean nothing to the IMV. Put that information in the description and ask more if you want. But all that maintenance work you put into the vehicle, you will not recoup that. The car needs those part to operate safety and had them to begin with, so they are a none adder. Having them replaced might help you sell it fast is all. That's why I usually sell my vehicles as is, as you never get back what you put into the car to fix it up for sale. It's usually a wash.

Those items are maintenance not upgrades. They may help sell the car but they do not add value. Not that it matters now but I think you were ripped off.