Having stayed at both AllStarMu and POR, I would say you are fine either way. The beds are the same size in both rooms. POR does have a double sink vanity. But the toilet area at AllStarMu seemed to be a bit larger than POR. As to the size of the rooms, I didn't think the difference was all that great. POR is a tad bigger. The main pool on Ole Man Island at POR is much better (has a slide etc.) than the pool at AllStarMu. And the theming is more 'adult' at POR. My dd stayed at POR when she was 6, and again when she was 8. then last Dec., at 10, we stayed at AllStarMu. She loved it there. SHe loves POR but says the AllStars are so much more magical for kids. Her words, not mine!!! I would stay with AllStarMu and use the money for more good food.
But, then again....the boat to DTD is really nice from POR. The only issue I have with that is that when we went in early Nov they weren't running the boats. But I think they have started them up again for the cooler months. You won't go wrong either way. Have a terrific trip!!