In cases where there is a set value (Color DMD), or a properly installed factory upgrade (JJP Shaker Motor kit), I think it is more than fair to adjust prices accordingly, and is often a reasonable deal since it ignores installation time. I don't think many would argue that.
As for mods that have
subjective value, such as aesthetic upgrades, they
may add value for a subset of buyers, or even reduce value for others. Definitely not a given.
In other news, bolting parts onto cars or adding shiplap to your living room will probably not get you a 1:1 ROI either.
Edit: Now I really want to find a beater 1K pin and make it a personal mission to bolt as much stuff as possible onto the playfield before posting it on Pinside for sale at $20k under an alt account. Hmmmm.
