(I can think of a few individuals who would LOVE to do that).
Who? Do you really think they would love to invest in a "dying game" (coming from you) so they can add more content, when there is already a huge community of people doing that? I doubt any developer would buy the rights to this game unless it was chump change, but there is no point of making it that cheap if there's still a bit of money coming in from sales.
The game is ten years old, the best I could see happening is somebody making updates to the engine, but let's be real here, who would be willing to spend their time constantly updating it, for basically nothing. At that point you may as well build another game and sell it rather than trying to get sales from small content updates, from a game you didn't even create in the first place. They'd get sick of the game way faster than badspot has.