Anyway, back when i was in the car trade, we ignored mods when looking at a car for trade in purposes, especially mods which added nil value to the car. Even factory fitted options didn't help. I remember a chap had a VS SS as a trade in. this thing had been optioned to the hilt, and cost more new than a Clubsport. It was still an SS, and got the trade it value based on that....
I have a sneeking suspicion that when the deler put the car on the lot, the asking price would have been much more than a standard SS.
Guess when i was buying, my experiance was that they always play both sides of the transaction and that used car dealers must have been fishermen in their previous life
Back in the 70's, a GTHO was about 1/2 the price of a house near the city. IIRC, just before the GFC a GTHO sold for around $900K, about 1/2 the price of a house near the city...
So buy the car you want and can afford and if it tickles your fancy mod within the law. Just don't worry about resale value, you've already done a lot of dosh just driving a stock car out the showroom.
Possibly, in 40years, if your still around, it may keep up with inflation and you can feel comfortable in it's price... if your lucky and still around. Even then, stock standard seems to command a better price than joe blogs modded....
So "carpe diem, quam minimum credula postero".