Performance of 2D Apps on mobile: Optimizations?

We recently published a 2D App created using Unity Pro 4.6.2f1 (including iOS Pro / Android Pro). We are seeing it perform sluggishly on all but the higher end devices (including iPhone4S and below along with a wide range of Android devices). We optimized many areas, including creating sprite sheets for specific areas, not rendering items completely hidden behind other items or off-screen, and limiting FPS to 33. Could anyone suggest some additional optimizations that can be done on our end to improve performance? Also, does anyone know of any updates planned that would greatly improve the performance of the 2D UI system for Unity 4 or 5?

Thanks all, Mike