I was going to say the same thing as Laserman. After about 70-85% DVDShrink's on-the-fly compression is not nearly as good as a re-code with something like DVDRebuilder. There's a huge difference in quality at that point.

Instead of going for visual difference between your new SL and DL transfers try something like BitRate View. Get the average and peak q values of the elementary video streams (before authoring) for both the SL and DL encodes. That will give you a better reference as to the real difference between your two versions.

Laserdiscs, even PAL, are soft (up to 5mhz analog, thats like 544x576 digital resolution) and the q values end up quite low. That's why I re-coded Moth3r's to allow for PCM audio, there was minimal difference in quality if I had used a DD track and put the extra space towards the video.