Mermod,
I thought Vestibular vertigo was bad enough but not so.
You need to find a good neurologist and as you say maybe on the mainland, Melbourne perhaps.
Success rate with ops is everything, however if it is effectively altering your quality of life and there is no possibility of improvement or you are unable to minimise the effects, an op may be your best shot.
You are still young and medicine is making advances all the time, without being a wet blanket anything to do with Vestibular doesn't bode well. Catscan and MRI if not already done, will clarify what is going on.
Good luck and take it one day at a time, as all else has to fit in with that.