I also owned a Nexus 7 (the same 2012 version as yours, not the newer 2013 one), and it was my first "eBook Reader". It was nice to use in the early years, then later it started to freeze up frequently, requiring reboot. At times even simple reading of ebooks was a pain, and jerky. So early last year, I started searching around for a replacement - and bought myself a Nexus 9 in April 2016. It's not the top-of-the-line tablet around, but it's the best I could find for me at the time - within my price range and with fairly decent quality - I bought mine from an Australian-based online store at AUD$ 417 (before adding shipping cost).
My Nexus 9 specs:
- Made by HTC
- Out in late 2014
- 8.9in, weight 436g
- Resolution: 2048 x 1536, (~281 ppi), 4:3 aspect ratio
- 32GB internal storage, 2GB memory, no SD card slot.
- NVIDIA Tegra K1 64-bit dual-core processor at 2.3 GHz
- 4G LTE (but I only use its WiFi)
- battery: ~ 9 hours general use.
Like you, I am also primarily using my Nexus 9 to read ebook, as well as online news & articles. But I also use it to view Youtube - there are lots of online how-to's & tutorials on the Internet nowadays, and with my tablet I can view them in many more places than a PC. I also use it to listen to podcast or even Youtube clips.
One year on, my Nexus 9 still performs reasonably well for all the things I use it for. I had since upgraded its OS a few times, it's now 7.1.1. While not as handy as my old Nexus 7, I find its size and form-factor to be pretty good for e-reading - even US-Letter size PDFs. My eyes can't read small prints nowadays, so the ability to effortlessly zoom the font up really helps. With more memory and newer CPU, both reading and viewing of videos are much smoother than the Nexus 7. Started to have the occasional freeze up requiring a press-button reboot, but it's still few and far between ...
Now in 2017, I don't think the Nexus 9 can cut it as the new tablet of choice, unless of course you could find a brand new one with a price too good to pass up! I haven't found a need to root my Nexus 9, just yet. Though at the time, one of my reasons to go with a Nexus tablet is its reputation for being 'easier' to be rooted.
In fact, I found this site: The best Android tablets in 2017 ... FYI.
http://www.techradar.com/news/mobile-computing/tablets/15-best-android-tablets-in-the-world-905504
and not surprising that Nexus 9 didn't make it into the list. In fact, only one Google tablet in this list - the Google Pixel C (but it's too pricey).
Here you are, just my personal impression and experience using an Android Tablet - not exactly a most recent model, but close. As for a smart phone, I don't think I can offer any advice as I haven't been looking around for a new one since 2013, when I bought my Nexus 5 - still working well (touch wood!) ... and I intend to keep using it for some time ...
Cheers,
Wen