is there any way to test location-based services (Position::enableLocationEvents() and friends) in the simulator? Something like replaying a GPX file would be very useful.
You should be able to use the file playback option found under "FIT Data->Run From File..." in the ConnectIQ Device Simulator. This will play the positioning data from a provided fit file through the simulator. In the future we hope to also provide simulated position from the "Simulate" option in this menu, but it only supports sensor data at this time.
For best results, I recommend using a FIT file that was recorded with once-per-second data.