Breaking a Mob Spawner should drop the mob's drops.

When a mob spawner is mined, it should drop the same items that the mob inside drops. The greatest benefit of this is that people who play on Peaceful difficulty would be able to get Blaze Rods, making it possible to get to the End without relying on the one-in-a-trillion chance of an activated portal or changing the difficulty. Besides that, it just makes sense for a mob spawner to do this since it already drops experience when broken.