If selling the bike, I'll part out anything on it that I can sell for more than $50 or so. Installed on the bike, the parts impart very little value and really don't make the bike any easier to sell. When people browse ads, they have a number in mind for what the bike is worth given year, mileage, and condition, and any number much higher than that negates any benefit as far as added attractiveness of the accessories.
If I"m buying, I have a particular set of accessories that I'm going to do to pretty much any bike, with there being some differences depending on what I'm buying. If a bike has high-dollar stuff on it that is the exact stuff I'd buy anyway, then I'll factor that into my decision. Apart from that, I'm not paying $1 extra for 'extras' that I don't care about, regardless of their perceived value.