I didn't know that they bothered changing the back sprites for Plat and HG/SS. Which ones were updated? Also, just an opinion thing here, but I would personally focus on sprites that don't exist yet. Sure, the Gen 3 fronts and backs don't look great, and they look out of place when Gen 4 or 5 Pokemon are used. But there aren't back sprites for Gen 5 Pokemon that are really usable considering the change to fully body backs. That's part of the reason that I decided to only resize the front sprites when absolutely necessary for my project, simply because I wanted to minimize the workload for myself. After we have usable sprites for the new Pokemon, then we can go back and work on the old ones to maintain a consistent style.