Unless I am sitting in the 2nd row of seats (basically behind the side surrounds and in front of the rear surrounds), the two rear channels aren't to terribly noticeable unless I bump up their dB a little, and then it ends up too loud for the 2nd row people.
I am glad that I have them, but more for giving a larger surround field than noticably hearing those extra discrete channels.
Also, Mark is right on the ball with the VP160. I have the VP180 (purchased before the VP160 came out) and it is a huge improvement over the VP150 (which I had good success with too). The center channel being the most important in the home theater, it is not something to skimp on and the VP160 will fit the bill VERY nicely.
And yes, get the 60s not the 50s...
M60s, VP180, VP150, QS8s, M3s, SVS 20-39PCi, Shakers