I thought about it but in this case I do not believe that it would be any different. My issues were not with the speed of serialization but with the speed of the AutoCAD .NET API saving that information into the drawing database via ResultBuffers. Once I zipped the resulting xml file the speed increased dramatically.
** Edit ** Now that I think about it, the information serialized to json would be a smaller file size as json does not require as much extra information in its file. I just might look into this.