good question!
i can't think of any old Quad LP or tape that hasn't been bettered in some way by the beautiful Japanese 7" SACDs or Mr. Dutton's marvellous SACDs.
also Sony NY and Audio Fidelity both did some great Quad SACDs in years gone by that i also found were all an improvement on the old equivalent Quad records and tapes as well.
the thing to always bear in mind about Quad is that almost every consumer delivery format of the time was quite flawed in some way.
even the best format, Quad reel to reel tape, which could have excellent fidelity, speed stability and was fully discrete was expensive and unwieldy and limited to select releases by a mere handful of labels. if you desired Quad reels by CBS or ABC artists you were out of luck.
SQ and QS LPs could never reproduce truly discrete Surround sound and even though CD-4 could in theory deliver discrete Surround from an LP in practice the format had its own drawbacks and as for Q8s, well they are 8-track tapes at the end of the day and we all know about their limitations and deficiencies.