Sounds like a fun car Wayne.
#1 on the list is slow down when you're not showing off.
The aero is horrible on that car, so anything you can do to slow down will help. Also, you don't have regen, so avoiding brake use is another huge benefit, even (actually especially) at highway speeds.
As for mods, I'd start with finding an increased tire pressure you're happy with. Then I'd make a full grill block. If you don't want to effect looks, do the blocking from the back. The next thing I'd look at is some sort of air dam for the front bottom side of the car. Unfortunately after that you're going to start having to effect looks which I doubt you want to do.
Also, what are your rpms at highway speeds? If the motor isn't spinning fast enough you'll have a reduction in efficiency.