Is there a thread I can follow or some list I can subscribe to, to get notified when the GameSparks Unity SDK is updated?
This has been implemented into the latest Unity SDK which you can grab here.
With it you can update it from within the Unity Editor itself. When you click in the GameSparks settings window the latest available version will be displayed in the log.
In the settings window in the inspector you can simply click "Update SDK" to update.
Thanks for the suggestion. I've added this one to the backlog, I'll keep you up to date with any news relating to this.