You have to consider that you are selling to the trade though to be fair. As a private seller on a high value car/vehicle it's often hard to compete. The trade for most part is more interested in selling you a financial package hence a cash buyer is not really in their best interest. As you mentioned, Teslas profit per car are higher so they are not fussed either way.Compared to the original new price, basically the price I paid minus the price I'm being offered for it by WBAC etc divided by the number of months owned.
Personally, I just rite the money spent on vehicles off as in not to be seen again. Historically, each car ive bought has been more expensive than the previous and imho it's the same analogy as saying a conservatory, house extension etc. is an investment. Probably so if you are a property developer but if you done it to enjoy it and plan to live there forever, this way of thinking is null and void.