When Ram finally has the 6'4" bed available with Ram Box, and Patriot Blue with Walnut Brown Metallic is available again, I'll definitely order the 12" display, just to have the vehicle be a bit more current and a bit more "future proof".
For navigation, I use 95% just audio instructions, listening to the instructions and watching the road signs ahead. I glance at the display only very occasionally to see which lane I should be in for an upcoming freeway transition or turn. But when I do need to glance at the navigation screen, I know I'll be very glad to have the 12" screen, much easier for my older eyes and slower brain to quickly get a bead on the larger map image.
For me, my audio needs are not great, I just listen to the few over-the-air radio stations I like. And whenever the wife and I are in the same vehicle, she handles all of the audio via Spotify on her iPhone. If I don't care for one of her song choices, I just tune out for a few minutes until it passes. So a giant display for audio is not a big requirement for me, but I love the larger display for the vehicle camera functions and, as mentioned above, the occasional glance at navigation for an upcoming directional change.
So definitely the 12" display for me whenever we can finally order exactly what we want. The way Ram is having trouble keeping all options available, I'm guessing not until March/April 2019 timeframe.