I am curious about line conditioners.

I also found the biggest improvement was in the quality of the video in every respect. I also experienced something similar to Elizabeth. For fun I connected my Vansevers Reference conditioner from my audio system to the Video system and found the colors became too vibrant, almost cartoonish.
I probably could have adjusted the settings on the TV to tone it down, but it was already perfect with the conditioner I was using (Audio Power Pack II).

PS: I recommend you get a conditioner with dedicated Digital AC inputs. The Video will perform best with digital AC conditioning from my experience.

The PS Audio stuff is very nice. Just be sure you want to afford the 500 watts of power it uses (the smallest model). I assume the bigger ones draw even more power.