Basically if you read the various posts on it - the opinion seems to be as follows:
1/ From 1972 to 1982 it didn't have most of the top players - hence it was a lesser event
2/ 1970 only - very few top players attended.
Basically, it was a top event in 1969 & 1971 - having deep fields. Then in 1983 the top players started to come back again - had Lendl, Wilander, McEnroe etc at that event.
In my opinion 1990 is an arbitrary division.
From 1983 it was a great event again. In 1988 it went to hard court and a new stadium. There was no difference in the quality of the field in the field comparing the late 1980's to 1990 and beyond.
1968 it was still an amateur event.
So in Summary - strong event from 1983 onwards, but also 1969 & 1971 it had true Grand Slam status.
1968 prior it was certainly a strong amateur event with the likes of Emerson, laver, rosewall, hoad winning it.
By the way, check out pc1's excellent comments about the Australian Open in 1983 - just recently posted post number 235. It really puts it into context: