I owned a pair of Studio 20's in the 90's. They were detailed, excellent mid-range and better bass if they were loaded with 'sand' or 'buck shot'. They imaged very well, for example the height of a vocalist. They had great finish and build quality. I think it was poor decision on my part to sell them. If I see another pair of 20's, 50's or 60's I will buy them.
The current MA line doesn't seem to have the same build/part quality. MA now has a different build strategy focusing on global marketing with cheaper components. The cabinet build quality is extremely important not just for cosmetics but better sound - Sonus Faber, Wilson Benesch are good examples - the extra care & time spent on varnish, lacquer, etc has very specific purpose other than just cosmetics. The current MA line-up just looks and feels mass-market and consequently lot cheaper to manufacture. The sound signature of the GR line is about personal taste and you may rightfully believe a GR60 is superior to it's older counterpart. OTH as someone previously mentioned, those special speakers or any 'used' time-tested product is always difficult to get because it's in high demand. For instance, always difficult to find a used pair of Sonus Faber Extremas, Guarneri or Electa Amator II's - they are all out of production for many years but still considered exceptional performers. When they're listed anywhere, they won't be around for very long - that's a sign of strong value - because they are not just a pair of speakers but real work of art.
My vote goes to Studio 20, 50 and 60 over the GR's.