The 'best' way will depend in part on your current QFF status. If you purchase a discount economy ticket for $2000 that includes car rental valued at $1000, you can earn up between 20 486 and 40 972 points for the return journey. That may be enough to get you a return trip to NZ or Fiji, or around 35% of the points required to get you a return Sydney-Frankfurt.
Alternatively, you could purchase the return ticket at $2000, and use your existing points for an upgrade to business (currently 100 000 return, but from 1 January 2004, 180 000 return). Rack rates for QF business to Frankfurt are at least $9600, and you would still earn at least 20 486 points.