I have figured out how to refine the AeroFly mesh for the U.S. quite easily using USGS NED data (publicly available). It's a pretty serious improvement on the default AeroFly mesh, especially for valleys in mountainous terrain. This data is available for the entire contiguous U.S.
For those who are interested, I'll be posting a how-to here in the next couple days. You'll need another program called QGIS (open source, many of you already have this if you're geoconverting already). It's easier than converting aerial imagery, and can be reversed by simply deleting the files you create from your Documents folder.
I was asked to put a disclaimer so I'm saying it now, and will repeat it again when I post the tutorial: do this at your own risk, and if you edit the terrain meshes for some of the default airports, it might break certain things about them. I haven't tested already-developed areas enough yet to know if this is likely to happen. In my opinion I think this is very safe and is just as easily reversed, but know how to do the reversing before you begin!