Speaker cables would make a difference on mid-fi systems and up, with proper equipment set-up. In my experience, more likely changing the sound signature and adding a flavor, similar to equlization. The biggest difference I've discovered though, was in power cords, primarily with tightening bass frequencies and adding (or detracting) music body weight
How high end must your system be...
...for you to be able to notice the differences different cables will make. I've always said that I have ears of tin until a friend of mine came to my house and said that my system was just not high end enough to be able to hear the differences different cable will make. My system isn't the newest but it wasn't that cheap. My system is valued at several thousand dollars and I don't think I have anything in my system that you can find at just any audio store.
So, how high?
So, how high?