Just to add another reason why tiled-sliced sprites are a good thing compared to the 9 pieces solution, tiled sprites need to have a very weak compression (like 32 bits), or there are artefacts at each repetition of the sprites (when compressed to PVRTC4 for example) ; if only the center of a sprite is tiled, this problem won't show up anymore.
Edit : And even with a 32 bits compression, there are still artefacts when the tiled sprite is used as a image button or when it's dragged... I think I'll go with your solution Nicki (I think it will fix all this), but it would have been better if it was included in the officiel package for the updates.