I'll be in Melbourne Aug. 9-15 for business and want to make the most of my LONG flight from Vegas. Wife and I (60) can arrive in Sydney on Aug 4 and am looking for suggestions for number of days in Sydney and is it worth it to take 2 days and drive to Melbourne... and, if so, where to stop?

I would stay in Sydney and take day trips to the Blue Mountains etc. from there.
http://www.visitnsw.com/sydney.aspx

I second Downunder on that. Sydney will be much better weatherwise and spending time there and surrounds would be much better - then fly to Melbourne.

But we are scheduled to stay with friends in Tura Beach Aug. 7+8.

I assume you mean Tura Beach near Merimbula (about halfway between Melb and Sydney) which is a 5 to 6 hour drive from there to Melbourne. It's a scenic drive for parts and you would see lots of the country and country towns but would you want to leave there and drive to Melbourne for the conference in that short time frame?
You could fly from Merimbula to Melbourne after Tura Beach.