Moving from the VP180 to VP160 your trading off higher power handling and better dynamics due to the dual driver complement of the drivers in the VP180 to better off-axis performance of the VP160, particularly in the horizontal plane.
I have heard both and in comparing the two, I believe your assessment is pretty accurate. I ended up buying the VP160 because of size and weight issues and I would also concur that it does have a "slightly" better off-axis dispersion than the 180. The 160 is still a big "full-range" speaker that would meet the vast majority of any A/V requirements. The reality is these differences between the two are subtle and a matter of taste.
For those looking to upgrade, in my opinion, there is a much larger difference in performance between the VP150(which I also owned) and VP160 than there is between the 160 and 180.