Test tones are a bad indicator of tonal balance. Just having speakers in different positions can make test tones sound different. Even identical speakers like my front 3 M80s sound different as test tones play on them. The best way short of demoing one to see if it might make a difference is to play a phantom center with your M80s. If you hear a noticeable improvement at the sweet spot in the center channel played in stereo on your M80s then you might benefit from upgrading to a VP180.

3M80 2M22 6QS8 2M2 1EP500 Sony BDP-S590 Panny-7000 Onkyo-3007 Carada-134 Xbox Buttkicker AS-EQ1