GregM,
You have to ask yourself what kind of movies and TV you watch. If you watch a lot of action movies and TV shows with quite a bit of audio in the surround channels, then you will notice the biggest improvement going with the QS8's first.
On the other hand, if you just watch a lot of movies and TV where there isn't a lot of use in the surround channels, then you will see a bigger improvement going with the VP180 first.
Since I sit in the sweet spot and my wife could care not care less if I have Axiom speakers or use the ones that came with the TV, I find the center channel to be the least important speaker in the surround speaker setup. In fact, you can use a phantom center channel and not lose much at all sitting in the sweet spot. It is only when you want to sit a little off axis that it becomes more important. I too, want to replace my VP150 with a VP180 since it is definitely the weak link in my speaker setup, just like yours. But, it will probably be the last thing that I would upgrade. I would like to upgrade my Outlaw sub to something more serious first. Then replace my M22's with some tower speakers. Then replace the VP150 with the VP180. Then go to heights and widths, if they are still around a few years down the line.
