TBH, I've never sat behind my rack and treated the entire system as other members do. I kind of do it piecemeal so I'm not sure if I can hear a difference.. But the cleaner works very well. To answer your question, after cleaning the speaker cables and speaker binding posts I really believe there was an improvement in SQ. The cloth I used had some major black spots from removing tarnish.
The Deoxit Gold coats the metal after cleaning and is said to increase conductivity. Many good reviews about this product. There are other contact enhancers that some members swear by.