http://www.porcelainmarksandmore.com/germany/saar/mettlach-01/

Here is a history of the company !! I think your mark is a variation of 2-17 shown above !! The only difference is the name at the bottom !! The one above shows Mettlach and yours shows Wallerfangen !! I believe they were just different places of production !! Perhaps Chris will take a look and give more info however his site has a pretty extensive history !! Yes there will be some value but I do not think any great amount !!