In the 1970/80s when not all top players played Australia was it still called a Grand Slam? And did top players ever talking about winning all 4 'slams'?
If not when did the usage of the term grand slam become common in tennis, and what changed that made Australia suddenly so prestigious?
Australian was prestigious tournament, but well - the same can be said about some "500" current tournaments. Was it at least 4-th the most important? No, strongest players were playing Masters in that weeks and I believe it was 4-th Slam those days. I can advice you to read Mcenroe`s book.
Journlist John Kieran is widely credited with first applying the term "grand slam" to tennis, to describe the winning of all four major tennis tournaments in a calendar year almost eighty years ago. About so prestigious can`t say 100% correct, but from early 1980-s top players began participating there again. Maybe it wasn`t reason, but consequence - don`t know.