I couldn't agree with this more. Aside from most of these quad mixes being demo-quality material, they range between difficult and impossible to find in Q8 form, and go for a lot of money when they do show up. On top of that, a lot of the stereo versions of these titles only came out on CD during the peak years of the loudness wars so the only digital versions that exist have their dynamic range squashed and don't sound very good. These are the DR ratings of the stereo CD versions of the Isley Brothers and O'Jays albums that also have quad mixes, from my collection:
The Isley Brothers
1973 - 3+3 DR9
1974 - Live It Up DR9
1975 - The Heat Is On DR11
1976 - Harvest For The World DR11
1977 - Go For Your Guns DR9
The O'Jays
1973 - Ship Ahoy DR10
1974 - Live In London DR11
1975 - Family Reunion DR13
1975 - Survival DR9
1976 - Message In The Music DR12
Judging from what I've heard on vinyl, the Isleys stuff should be at least DR12 for the earlier albums rising to DR14 or 15 for the later ones and The O'Jays should be similar values, although maybe 1 or 2dB less. The Isleys remasters seem to suffer especially from really bloated bass on top of the compression too. This would be a golden opportunity to finally hear some of these albums in their full dynamic glory!