Heh, Im not even mad that everyone has an opinion, even if its wrong, given that this is a public forum, LOL.
For rebuilds you usually take the "fair" condition value, or the lowest value of the KBB as a rough estimate (which is what I am asking for it). Now this definitely depends on what was wrong with the car to begin with, obviously if the car had frame damage, flood damage, or other serious damage than that goes out the window, and you probably shouldn't be buying a car like that anyway. If we are talking light skin damage (fender, bumper, core support ) then this holds true and this is what was damaged and replaced on this car.
In addition, I realize that you usually do not get your dollars back from the mods that you put in, but I am offering a problem free car, with about $4K of upgrades in suspension, and $2K in performance upgrades for the price of a "fair" condition Z with high miles.