Just to add, I've started experimenting with using an exporter in my current project (admittedly part way through, so the final result will be a bit split between methods, but this particular part requires some complex data structures, so may well benefit from this approach).
To clarify my previous comment - I now understand that the idea is that you don't make the exporter subclass templatable, but instead, you have a templatable class, which then instantiates an exporter instance, to generate the data (although, in my case, the templatable class ends up being only a fairly thin wrapper around the exporter).