While I'm not overly concerned about factory original, I have nothing but respect for the folks that take the time and effort to do it right.
That being said, I do appreciate documentation and relics from the car's past.
Frinstance, I was lucky enough to find the Body Broadcast Sheet under the back seat:
I keep it in a plastic sleeve inside a three-ring binder, along with pictures, receipts, registrations, etc.
I also did rubbings of the buck tag and used the VIN analyzer on this site! Found it was originally Aegean blue with a black vinyl top.
I also have the owner's manual for my Mustang:
With the original owner's name typed in by the dealer:
When I disassembled it, I found some Faygo bottle caps inside the quarter panels- OLD ones, bent by a church key with the cork gasket inside it. I'm guessing they were tossed in at lunchtime at the San Jose plant! I kept those too.