I preordered a 2012 N7 when it first came out, used it pretty heavily until I got my preordered 2013 N7. I feel like it was definitely worth the upgrade. The screen is much nicer: brighter, more colourful and of course much more dense in resolution. The battery life is significantly longer, especially in light tasks (heavy GPU use will consume the battery faster in 2013 N7, but this can be forgiven for the 5x increase in performance).
General performance is much more snappy. In the 2012 N7 I often encountered lag when switching quickly between apps while installing stuff in the background etc. All this is gone on the 2013 N7. The extra NAND speed is nice too, opening and installing stuff is noticeably faster.
The device also has a nice build. You can definitely notice the thinner and lighter body, and it feels much more solid than last years model.
The only real issue I had with mine was a 'pop' in speakers from touch sounds even when muted, but disabling touch sounds in Settings fixed that. Haven't had any other hardware issues (reboots, dead pixels, dust etc).
Only thing I dislike (very minor) is that it doesn't have a Snapdragon 800 like the new Kindle Fire (same price). This wouldn't affect real world use, it's just an e-peen thing.
Basically, I can't really see any reason not to upgrade.