If you can support smaller texture sizes, the memory and bandwidth on GPU will be much better. In practice, it depends a bit, because if your texture is too small, the quality might not be what you want. In general, though, you won’t gain anything by scaling textures up in advance, let the GPU do that and it should be a lot better.
Scaling down, however, you can get a quality and performance benefit by scaling your
BitmapData first, so that you are sure the smaller graphic is smooth, and so that you have less texture data to upload