You only need to ask yourself a couple of quick questions.
Does dialog sound loud enough, clear enough, and is it properly "anchored" to the screen? Can I hear it sufficiently from every seating position? If you answer "yes" to everything, then I say no.
I have a VP150 and to be honest, 80% of the time, it is not being used. The 20% when I'm using it for HT, I run it at -2dB below the fronts. I have only 2 good viewing positions, so I often wonder is a VP100 would have been OK. My guess is that it would have worked fine. On the ocassions that I play 5 channel music, it blends in so well that I really can't judge it by itself. The whole "wall" of music sounds great, though.
Unless you have a problem you can hear, I would stand pat.
