There are three nitro off-road tracks in the Brisbane area.
Pine Hills Dirt Racing is on the northside. Details at
http://www.pinehillsdirtracing.com/wordpress/
Logan Offroad R/C Car Club is on the southside. Details at
http://lorrccc.com.au/
and Sunshine Coast Offroad Club just south of Caloundra (on the sunshine coast - north of Brisbane). Details at:
http://www.facebook.com/groups/scorc/
All three have history of good tracks and competitive racing.
There are also EP10 offroad tracks at Redbank (chargersrc.com) and on the Gold Coast (indoor, clay) -
http://www.gcrcraceway.com.au/ . GCRC is awesome.
I believe there is also an offroad club in Toowoomba (about 1 1/2 hours west of Brisbane).
There are multiple EP and GP on-road clubs in Brisbane also.