|I live in Nati (Arapiles) and I get the hell out of here in July and August! In a good year (such as most of the last 15 whilst we had El nino and droughts) you will get a reasonable number of sunny, not too windy days between 10-15. These are the days people remember when they wax lyrical about climbing here in winter. They are not however, normal. In a normal to bad year (such as the last 2) it will be predominantly drizzly, cold, windy and generally miserable. I believe the BOM are tipping another one of those years this year.
SE Qld is a great place in July/August. Temps in the early 20s, and it's their dry season. Although you might get the occasional annoying colder or wet day. Ocean temps much much warmer in NSW/Qld (there's no land between Antarctica and and the SW Vic coast, suitable only for entering when it's about 40 degrees in my world), you can wander on further north to sea kayaking in the Whitsundays, snorkling on the barrier reef, if you get as far as Townsville, there's rock worth climbing again.
I'd plan a trip to Vic for spring or autumn. Don't stress about crowds, it's been super quiet around here even whilst half the Grampians are closed. Won't compare to many US crags. Except next week. Have I warned everyone to stay away next week? The Grampians might be a better option for anyone wanting peace and quiet and to avoid groups of kiddies on easy routes.