One of the things that was bugging me was that one of my objects contained a dictionary of subobjects, and the XML for it wasn't very pretty:
After much mucking around with Reflector and the documentation, I found Microsoft.Xna.Framework.Content.ContentSerializerAttribute, which has a number of properties, including 'CollectionItemName.' Changing my dictionary to a list and applying this attribute has produced a much nicer result:
On a related note, this is the first time I've actually used Reflector, and I'm amazed. It's a truly awesome tool if you're doing .NET work.