If the aircraft was controllable, an immediate return is not necessarily required, however, fuel burn off can and does affect CG position in flight. Stuffed if I know how the 717 reacts, but in my RAAF days we had to calculate a TO weight and CG position, a landing weight and CG position as well as a worst-case ZFW CG position to make sure the aircraft wouldnt go outside the envelope in case of fuel exhaustion.
Melbourne probably had better connections for the passengers too but I doubt that would be the main concern.