Here's the way I see mods:
- If you have normal bolt-ons it doesn't add much if any value. An intake or exhaust does nothing for me because the vehicle needs one, regardless of the brand.
- New parts are more desireable than old parts. New lift, bushings, wheels, tires, etc are worth something compared to worn stock parts, so the price should go up accordingly, but not by the amount that the parts are worth pre-installation.
- Added parts like a supercharger, bumpers, winch, are worth something, and that value is based on how old they are, perception of how the vehicle has been treated, etc.
- Modifiying a vehicle limits the number of interested buyers.
- If you're not in a hurry, you can possibly get some, most, or more of your money back out of mods, but it might take a long time. If you just installed the parts, there is a better chance of the latter two being true.
A lot of people who are buying vehicles try to live by the, "mods don't make a vehicle more valuable" mantra, which isn't usually true. You just shouldn't mod your vehicle and think that you are increasing the value by $1K+ everytime you spend $1K.