I did one full day on GOR, slept, did another half day on GOR/half day in Grampians, slept in Grampians, did another half day in Gramps and was back in MEL by late afternoon. Didn't feel we missed much, if anything.
Besides, even if an argument could be made to do a second night on GOR, I'd rather skip whatever we may have missed and have more time elsewhere.