I would have to say that on a scale of 1-10, the different wire pulled it up a full point. Now that my ears are a little more discriminating, I'd give my system a full nine out of ten now.
I have the v.2-400's and I admit, the fronts improvements are not very apparent as far as I can tell. The rears are an entirely different story though. The extension wire that I had used were 1/8" plugged that I added to the ends of the rear wires. As I realize now, they were total crap.
Based on your experience, if I didn't used extensions, I doubt that it would be worthwile.