Retexture the canopies so you see some light scratches/swirls, especially when looking toward the sun - throw in some faint reflections from parts of the cockpit/pilot as well. Maybe that's too much to ask for
I thought that if the oil effects are present, adding something like this might also be possible.
I think it would add to situational awareness when you're dogfighting, using those canopy cues for info about position.
Falcon 4.0 has these effects and I think it looks great.