I did own an N9 since launch, and I picked up a PixC at launch too. My N9 served no purpose except as a media tablet. Youtube, Netflix and locally downloaded content (particularly when flying). No productivity at all.
When I bought the Pix C, I expected it to do that same thing, with the small added exception of the occasional email. I bought the PixC + standard
As a media tablet, the PixC is indeed better than the N9. Screen is much better and brighter (though, to be honest, if you had a Nexus 9 that never went side by side to the PixC, you'd be perfectly happy with it), battery is much stronger (no contest) and the speakers, while a little bit tinnier than the N9, is indeed louder in most scenarios (just by a hair). So for most online video consumption, it is the better device. I found myself grabbing the PixelC time after time.
After a short while, I started using the PixC for a little bit more productivity, the odd email here and there, etc. But, last week, I had a revelation. I had a work trip interstate, throughout the day, the Pixel C did everything I needed it to do - bar 2 hours for a presentation that I did via my MBP. All in all, the SOT for the Pix C was close to 9 hours by the time I got home (4 hours of streaming video on a flight, plus 4+ hours of emails, browsing, google drive, etc). It still had 30% battery remaining when I got home. It replace my MBP nearly all of the tasks that day, with very little detriment to efficiency - granted, I didn't require too much multitasking.
What this means for me is that, I can now bring my MBP + Pixel C on these business trips, with no charger, have a full day's entertainment, not have to look for a wall socket, and be perfectly confident that I can do a full days work as well, and not run out of juice. For comparison, my MBP runs about 5 - 6 hours with my typical usage, so if I used it for 4 hours on the flights (2 there and back) plus my 2 hour presentation, I would definitely require a charger for the day, AND be on the lookout for a wall socket.
The PixelC, whilst not perfect, definitely fits in with my lifestyle