For me it's not the fact that they are simply incredible entertainers, but that both Kevin and Cindy are genuinely nice people. Don't get me wrong, They will stand up for what they believe in and when FOX made it their position to blast illusionists by revealing their trade secrets, Kevin pulled out all the stops to not only protect his business but to protect other illusionists and the legendary art form itself. It's kind of like watching how they make specific parts of a movie. Once you know the trade secrets, you never enjoy a film the way you once did.
Illusions are an escape from reality.
It's like watching a movie with incredible special effects. You appreciate the skill required to pull the whole thing off. With the Spencer's illusion show, incredible feats are performed in front of your face. We know people have an innate curiosity about how things work. People are drawn to magic to escape from the hustle and bustle of everyday life.