Quick update from the previous post: I decided I wanted to add more detail to my map by showing small pie charts instead of markers.
After trying and failing to use Google's old Image Charts for the marker images, I found a very neat solution on StackOverflow that solves the problem nicely by rendering Google's new interactive charts onto a custom overlay above the map:
I then added a piehole to make overlapping charts easier to see:
Passing in the extra data was also a slight pain because I needed to use a Dictionary
Next on the list is showing more details when clicking on the graph.