IME experience ANY fare is eligible for a Standby upgrade... paid for with A$ or Certs...
It is the Confirmed version that requires higher fare classes...
I bought one of the sub $1000 SYD-LAX rtns... and have applied for A$ upgrades Y>J on both long hauls without a problem.... (will report back on whetehr I actually get 'em!)
P.S. Unless they are the only flights available I'd NOT use the certs Trans Tasman!!!! Much better value Y>Y+/Y+>J on long haul... (or Y>J using both!!^)