Mine has seats, steering wheel, pedals and all sorts

and new R32's were £18K recently...
Typically, you get very little for optional extras/add-ons come re-sale...
As much as it pains me to say it: trade £15k (depending on how desperate the dealer is), private £16.5K. There are still plenty of unregistered examples around and you will need to differentiate yours in price terms from a 58-plate whether or not you have extras