I'm sorry to say that there is no support for Write at the moment (I added it in there hoping to get it implemented but never did...)
Looking at the code, it wouldn't take much to get it working if you wanted to have a go at it yourself?
WriteAttributes in SvgElement.cs appears to be the only method that hasn't been implemented. It could quite possibly just be a case of iterating though the Attributes dictionary and using TypeConverter to convert the types to System.String before writing
them to the XmlTextWriter.
Hmmm, I see why WriteElement is currently returning nothing. The problem is that ElementName is null and this only gets set during a Load and it sounds like you might be using something like 'new SvgCircle()'?
I'll have a think about how to best solve this issue and get back to you.