You know what? I've bought and sold quite a few firearms and the single biggest thing I have learned is this: as a seller, you will likely never see the real value of accessories on your item as compared to if you stripped them off, and sold them on their own.
I think it really comes down to the fact that folks want to put their own crap on their new firearm. If your Seekins has a Geissele trigger in it (call it 200.00 retail). You could maybe ask 100.00 more for it, but if you took the trigger out, sold the Seekins with a standard trigger and sold the Geissele separate, you could likely get 150.00 or more for the trigger alone.
That's just been my anecdotal experience having done this for a while now. If you'll notice many of the rifles on the Hide that come with an optic don't end up selling as one unit. The seller ends up getting a buyer for the scope, and a separate buyer for the rifle.