There are two reasons to consider upgrading your center channel:

1. You hear tonal shifts that bother you.
2. The VP50 can't fill the room adequately, and the receiver clips when you turn the volume loud enough.

If you're otherwise happy, don't bother. Though its specs say it's a sensitive speaker, the VP150 is starved for current, and you might find yourself needing to pick up a separate amp with your modest receiver.