In another thread, reese makes a very interesting point and comment:

They weren't like the Shirelles, who basically joined the oldies circuit in the early 70s and have stayed there ever since making a good living. By comparison, the Supremes still had a contemporary presence and wanted to be seen as such. But to do that, they needed hits and had to bring in others besides the die-hards.

Do you think that if the Supremes had tried to be less contemporary, and more "oldies", that they would have had a greater success in the late 70's? Just go ahead an embrace the 60's tunes, come out in the 60's dresses, and have fun with it? The could have hopped on the circuit, and maybe even made an appearance on the MIDNIGHT SPECIAL much like the Shirelles did.