From what I've been reading on the net over the past year from many so-called 'experts', the content to the CC in most movie mixes in the past couple of years has shifted away from just mostly dialogue to much heavier & complex content. Some say 70 - 80% now comes from the CC with the L & R Channels idling much of the time.
Based on this, I was able to justify in my own mind upgrading from a VP100 that performed very well to the much more capable & outstanding VP160. I'm glad that I did...
I don't believe that they have shifted anything away from the L & R channels, but rather started to put more than just dialogue voice into the center to give it more fill. But all that said, the bulk of dynamic sound still comes from the left and right.
Congratulations on getting a much better speaker for your Center. But I would not call the comparison of your move from a VP100 to VP160 as being a simple version update. Those two speakers are sonically miles apart. Sort of like going from a Porche Boxter to a 911 Turbo. Same company, but totally different beasts.
As for the upgrade program. I believe that if you waited for an extra year, you will get less back for your current v3 speaker than if you did the upgrade right now.
As others have said, if you are listening to something that is very demanding on the center channel at high volumes, such as 5.1 music, then you will get additional benefit from upgrading your center channel to the newer version. But, you might also get an equal bump from upgrading your amp if the one you have doesn't have the true power to fully drive the 4ohm speaker.
I have also been told that you can get far more bang for the dollars spent in adjusting yor acoustics.
There is no hard fast rule to any of this.