I suspect that most of the high prices you see on eBay are paid by people who just need a few last pieces of the puzzle, and that the cost is not an issue at that point. I might be wrong, but if you only used parts from eBay to put together a whole car, it would be one hell of an expensive car and you would never be able to get your money back when you sell it.
So I don't think that an accessory like that will make your car very much more valuable. Easier to sell maybe, but I really don't believe it will bring $3,000 more than it would without it. In my experience, parting out a car usually brings much more money than selling it complete, so if I could get that kind of money for it, I'd sell it in a heartbeat. Just my 2c.
