As I understand from Wine's policies, functions should only be implemented if an application requires them. If that's correct, a random search for stubs isn't a good idea, because the follow up question would be "which application requires this function?".
We certainly prioritize functions that an application needs, but we don't prohibit code that doesn't identify an application that needs it. It's true that we often ask on this mailing list which application needs a function, but I think that's generally when a patch looks strange for some other reason. One of the usual reasons is that it's lacking a test.
So, going back to the original advice: if you can write good test cases for a function, then there's a decent chance you can implement it, and both tests and the implementation can find their way into Wine. If you can't write good test cases, you'll have a much harder time getting your code into Wine. --Juan