Hey Scott, Generally anything that you add you’ll only get a fraction of that back on a trade-in. Retail might be a little better if you can find someone who likes all of the mods, but the pool is limited as everybody has their own personal taste. Obviously tasteful mods are the best...
Personally, I enjoy mod’ing and wrenching on all my vehicles, but I “try” to remove most everything before trading them in, which helps finance future mods. It’s a vicious cycle... ha. I just sold some things today off my Chevy that traded-in that paid for my Borla exhaust, which was more valuable than if I would’ve left it on the traded truck.
Certain mods, like lifts, are a PITA to remove. So you have to factor in the value of your time. Plus, you have to store all the OEM stuff, which isn’t too bad... unless it’s the factory exhaust that I now have sitting in my garage.