I completely agree with you PRiME! Though, you can reload the .js script with ALT+R if you edit the file externally, I always do it this way.
I've recently discovered that the FDM on aircraft can be reloaded as well without restarting the engine, by simply respawning the aircraft. Still not very practical, but I guess it's better than restarting Outerra.
Atm, the materials are the biggest pain for me, lots of restarts 'till I'm happy with the results...