According to Max I have imported 16500 entities into Max from GG. I removed all animated items, animals and characters before importing. When they had been imported anything that showed in the object library as a white dot or deformed was then deleted. More items will be deleted as I find problems with them. Yes many will not be super graphics due to age etc and even fewer will be PBR but it is better than consigning it all to the scrap heap. I prefer game player over beauty (DOOM) but much of it is still useable.
I do find Max doubles up on some assets when displaying them so the above figure is going to be lower but it amounts to about 50GB moved over at this time.

First thing is most of the Mega Packs were updated to PBR but if you are still on the original you will have to Un-tick the packs on Steam to uninstall the old ... Once done Re-tick and the updated packs will install.

Secondly if you find any you really like that do not copy and auto convert very well then re-import with the Importer which usually sorts the issue. I have tried most packs which seem ok but if anything the free classic pack is the one with old .fpi's and weird texture setups.