I have reinstalled on a new computer as my old laptop has decided not to boot. On that system I had added aircraft data, but not exported it. I have a backup of the filesystem, but can't find the aircraft data on it anywhere. Is it easily accessible so that I can import it into my new install? (I notice the User waypoints are there in xml format).

That folder is where settings are stored, which up until the forthcoming 2.0 release included aircraft definitions.

All chart, terrain and custom data, routes and logs are stored within your personal Documents folder, and beginning in SkyDemon 2.0 this is where aircraft definitions are stored too.