I was looking for a Discover Weekly saver for a while, but resorted to using just screencapping the list, and saving the good tracks internally.
One issue with saving a Discover Weekly list to Spotify is that Discover Weekly is generated based on the content in the user's playlists. If you add a bunch of Discover Weekly lists that are 28/30 duds you're going to start reinforcing the system to generate crappy lists.
I think that's why Spotify doesn't allow saving them. They do allow saving of the topical Discover Daily, which reinforces my belief here.
Just thought I'd let you know about the possible issue with your product. Even though I absolutely love it and would use it.