E38 models do struggle to appreciate in value, I'm afraid. Many buyers are put off by how big, complicated, thirsty and expensive the car is to maintain - but as a classic proposition (or at least a car that won't cover many miles) there is a case to be made for them. Consequently, an example that's in need of some TLC can go for well under a grand while we've seen one-owner cars with FSH and more miles than yours go through auctions for £4k. Ultimately, a car is only worth what someone wants to pay for it - but it sounds like your example should be at the higher end of the spectrum. If you're in no rush to move it on, ask for £2500 to £3500 and wait it out.