The Nexus 7 seems like an ideal size for a nav unit, just big enough to be useful, but not too big to be cumbersome, as well as reasonably priced for the size. However, I recently upgraded my phone to a Samsung Galaxy Note II, which has a nice big (for a phone) bright 5.5" screen, with 1280x720 resolution. So, while interested in the nexus 7, I didn't feel the additional 1.5" of diagonal screen was worth it, and jumped straight to the Nexus 10, which has an awesome 10.1" 2560 x 1600 (300 ppi) screen. While the N10 might be a bit too cumbersome for in-vehicle nav, it suits my everyday use better as I find a 10" hi-res screen much more suitable for web surfing, Netfllix etc. As far as internet connectivity, my Samsung Galaxy Note II has AT&T LTE, as well as mobile hotspot & tethering w/ 4GB data plan, and I also have a Verizon Jetpack 4620L LTE dedicated mobile hotspot w/ 10GB data plan, that has built-in GPS hardware (GPS position can be shared via WiFi), and a provision for an external antenna using a mini port on the side. So I can use either my Samsung Galaxy Note II or N10 on either AT&T LTE or Verizon LTE.
I already had my Galaxy Note II & Verizon Jetpack 4620L mobile hotspot for work anyway (I work at client premises, and like private internet access without having to rely on client guest WiFi), so the only additional outlay was for the N10, which I have got a ton of use out of already for general web surfing, Facebook, Netflix etc., so has already proven its worth for me, even before exploring using it for nav. I already have a double-Din head unit with XM radio & GPS on 6.1" display (and ability to input GPS co-ordinates in 1 format), so I don't really need additional nav capabilities for on-road use, but am interested in using my Android devices for offroad use. I have downloaded BackCountry Nav Pro to both my SGNII & N10, and have played around with it on both, but have yet to use it in actual use. MY SGNII has a microSD card slot, to which I added a 64GB microSD card, so no storage issues there. And, even if I wanted to store a bunch of music & movies, I could always purchase a second microSD card for those, so I have one dedicated to storing topo map tiles. I bought the 32GB N10, which is the maxed out version, but doesn't have a microSD card slot (unfortunate, but I think Google & others trying to push all data storage into the cloud are the reason for this). However, soon pogo chargers will be available for the pogo charging port, and then I'll be able to use the microUSB port on the N10 as a USB host port (using USB On-The-Go, USB-OTG), combined with a microUSB to USB dongle, and then I can connect as much data as I can fit on a USB thumb drive(s) to the microUSB to USB dongle, at which point my storage options are pretty much limitless. It's not quite as elegant as having built-in storage, or a microSD card slot that can take high-capacity microSD cards, but with a suitable microUSB to USB dongle (or perhaps even a 90 degree right angle microUSB adapter, if such a thing exists), it could probably be made to look pretty neat. The only question I have at the moment is whether to try mounting my N10 on my custom angled mid console between my armrest center console & dash (I think I'll just have enough space for it with some finagling & rearranging of switched on my custom mid console. The advantages are it wouldn't block the windscreen at all, wires would be neater & easier to hide, and it would be out of sight, so less of a potential target for thieves (though normally I'd be using it in the house, so would only be in the truck for offroad trips & easily removable anyway if parking in dodgy areas); the disadvantage is that it would require me to look down (momentarily taking my eyes off the road to view it). However, given that I already have built-in GPS in my double-DIN head unit, in my case I don't think that's much of a disadvantage, as offroad speeds are likely to be much lower & would mostly be used for trail breadcrumbing & occasional use when stopped to verify position and check surrounding terrain & route. The fun part is that events like the Baja 500 & 1000, and King of the Hammers (KoH) etc., which are relatively near me, have started to post Google Earth *.kml files of their routes (with checkpoints etc.) in recent years, so combining e.g. an Android tablet + BC Nav Pro + KML files + offline topo maps + built-in GPS provides for some exciting possibilities.