While blender doesn't make it easy to add a keyframe or driver to the NLA strip's scale, it is posible to create a driver by typing one directly into the value. You can type a simple driver to create it and then edit the driver once it has been created.
With most editable values in blender we can press I to insert keyframes, we can also type a driver expression straight into the value if we precede it with a
# as in entering
#frame will create a driver that uses the current frame for the value. For a random value you can enter
#noise.random()*12+10 to get a random value between 10 and 22.
You can manually add a keyframe (or driver) using python -
strip = obj.animation_data.nla_tracks['NlaTrack'].strips['DragonflyAction']
strip.scale = 0.35
Having said that - a better option would be to add noise to the initial animation and not to the NLA strip settings. In the graph editor you can add a noise modifier to each animated value.