Surely you've heard of ConFest? Still going strong since the 70s. Started by Jim Cairns (the then ex-deputy to the ex-prime minister Gough Whitlam). The name is a portmanteau of 'conference festival'.
> I just hadn't ever heard it referred to as "the predecessor to burning man".
But that it is :) It was a direct inspiration for burning man, and also another long running festival in Europe (the name escapes me).
> (And I've never been, Easter is BluesFest time for me...)
Are you talking about the one in Denniliquin that often coincides with ConFest? It's a very short drive away, and I recall bumping into a few curious folks making a detour after BluesFest.
https://en.wikipedia.org/wiki/ConFest