Max is right. If you capture a reduced luma range, then extend it afterwards with AviSynth, you can get banding effects. Conversely, the risk in calibrating the capture card brightness (black point) and contrast (white point) to grab the full range is that if something changes you may end up clipping the waveform. So it's important to check several sections, and to re-check when capturing the next side of the laserdisc.

You should definitely use the waveform monitor in the colortools plugin, because then you are not relying on your visual judgement or your monitor being correctly calibrated. I would say use the starfields as a reference for black rather than the letterbox bars - I remember a spot in Empire when the black level suddenly increased at a scene change, so the blackness of space became instead a washed out dark grey. And blaster flashes or explosions are a good reference for peak white.