You should never assume the value of a domain based on previous sales. It appears to me that the original sale was overpriced, i.e. the domain was not worth that much. It appears to be a niche target of 1 person to me, I don't think anybody would be interested other than possibly the person who bought the original. They now have the domain they were after, and .eu is not yet a strong extension, so they are not going to be as desperate for it as they were for the .de. Its a mistake based on assumption that I have made myself before- you need to know there is either one guaranteed buyer, or a whole load of interested parties possible, to give any value to a domain.
Sorry, I wish you all the best, and maybe if you are a really good salesman, you might get the previous buyer to take your domain too, but I would take what I could get for it if I was you, and certainly wouldn't expect the sort of money you are hoping for. Hope this helps
Kind Regards
Chris
