Bluetooth 4.0 is for sporadic bursts of data, not a constant stream that listening to music would require. When used in that regard, BT4 offers no greater energy savings than other flavors of Bluetooth (at least that's my understanding).
Seems pretty thick for an iPad mini. I would think Apple would be aiming for iPod touch thinness. This looks thicker than an iPhone 5. Also, the first photo looks wierd - like the logo & ports aren't centered on the iPad case.