[saand]

I have the same problems BLSTIC I purchased my car some time ago and didn't even look at the efficiency so here are some things i have done and am thinking about which might work for you
- Wheel covers on your rims
- remove non driver side windscreen wipper, im in australia as well and the roadworth says only single wipper is required on driver side. the VT may have the wippers out of the open airflow so many not be worthwhile for you
- remove side mirrors, roadworthy says only require a rear vision mirror, i drive changing lanes with head checks so never used my side mirrors anyway
- front grill block, if you put one on that is easily removable or can be changed to let some air through you can change it on the fly if your car starts to get hot
- If i was you i would be tempted to remove your rear spoiler and block up the screw holes, gives a bit of down force at the back, not sure how important this is for you
- belly pan, i have not been able to find cheap large coroplast in australia so i am going to try stretching cheap tarpoline see if it holdes up alright
- reduce weight, carpeting, floor matting, and anything in the boot could go. I also removed my AC but if your in the outback probably worth keeping that
- I am thinking of doing a change to manual steering. your VT might have electric assist in which case this would do very little for you
- Can try taping up gaps in panels if you are really getting serious
- antenna remove, replacing with well placed wires in the cabin may give same reception without the drag of the antenna that is in the open air

- I have also seen suggested a general tune can be a good idea depending if your efficiency has gotten worse much since you first started driving the car

- I cant think of much more than that unless you are willing to start changing your engine since yours is particularly large

good luck, i look forward to seeing what works for you and to see if you have any other interesting things i can try as well