Zero - vehicles depreciate big time the day you drive off the lot, no point in putting more money into a losing proposition.
You're right about depreciation, but if truely minimizing your cost of ownership was the goal you should'nt be buying new vehicles (or nearly new). Why not buy a base model vehicle that's many years older?... I'll bet you come out ahead financially with an older car, but we all have our reasons for driving newer cars and that comes at a price.
At least part of our vehicle purchase (in almost every case) is enjoyment/luxury/convenience, along with the part that is attributed to the necessity of traveling from place to place. Since 100% of the vehicle is succeptible to depreciation, some of depreciation that is from the necessary cost of ownership and the rest is depreciation of luxury/optional money that was spent by choice.
What's the difference of spending money on aftermarket parts vs buying a higher trim level truck with more options? It all depreciates and no sane person would consider it an investment. Do you have ANY options on your truck, or is it absolutely the most basic vehicle that satisfies your transportation needs?
Edit- I just noticed that you drive a limited... Clearly you have features that are well above the minimum required for transportation, and you choose to pay for that level of truck. Based on your original logic, every dollar you spend above the cost of an ultra-basic work-truck is money that shouldn't have been spent on a "loosing proposition".
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