One interesting point: you mention acceleration. The battery-only acceleration on the plugin prius is actually pretty acceptable. I recently rented a regular prius and my habit of accelerating as fast as I can without busting out of "eco" mode meant I was just crawling embarrassingly slowly, whereas in the plugin, you tend to outrun most average drivers if you do that.
The battery makes a big difference. Since it's just a helper on the regular Prius, it doesn't have to be all that powerful, and I think it's only rated for something like 30-35hp. On the plugin, it needs to be able to drive the car on its own in a reasonable fashion, so it's much more powerful, as well as the obvious thing of having a higher capacity.
Driving my Prius v, I'm battery-only basically when cruising on surface streets, sitting idle, or maneuvering around small, slow residential streets. And maybe, maybe if I'm accelerating away from a stop on a decent downhill slope with nobody behind me.
