I wish I had something encouraging to tell you, but I had the exact same experience at the Sheraton. They were frustratingly illogical and inflexible at every step of the way. Don't expect this to change - even when you are there for the wedding - they just didn't do anything to make things special or easy for us. That said, I thought my wedding was beautiful and I wouldn't do anything differently - except leave more of the planning and dealing with the Sheraton to my WC.
As for the cake, we had our reception at dCortez and they did the cake there and most of the guests said it was the best wedding cake they ever had. It wasn't that pretty or creative but it was really good (tres leches,chocolate, and vanilla). And way more than we needed (I think we all at less than half of it).