Question:
I'm looking into this same thing, but I would be using USB. My actual phone will continue to have the Bluetooth connection to my head unit.
Would it be better to have a large USB thumb drive, or even a mini-reader with SD Card, or would a phone actually serve the purpose better?
My phone doesn't have enough storage to hold a respectable portion of my library (32gb internal storage shared with all things).
Also, do you think it might be possible to have a Bluetooth Phone connection, and a separate device holding a Bluetooth Media connection? If I'm not streaming through my phone, I suspect Navigation won't pipe into the vehicle speakers. But if I did get a cheap phone with GPS and offline maps, could I use its BT connection to stream the music and utilize navigation while my main phone holds a BT connection for incoming/outgoing phone?
I'm trying to figure out the most elegant way to handle this. I'd really love to be able to use the USB cable I ran into the middle console area (could run it to the glove box) to charge my device, but that gets interesting if I have two devices. And if I don't use Navigation on the "media-only" device, then I really have no need to interact with it, save for updating the library. I would hide it under the center console trim and secure it to the side panels out of sight (under the cup holder assembly), and ideally, program it to cut most functions when the power feed is lost but otherwise remain on. Except for long times without driving, like vacations, it should have no problem maintaining battery between drives.
That's sort of the ideal method, imho, and I'd just use the 12v accessory in the center console storage bin to charge my regular phone.
If I do go that route though (hidden media phone), I lose navigation through the speakers (I think).
Ideally I'd just have a 64gb or 128gb phone - but dammit, choices are slim and then good stock or stock-like Android phones don't offer expandable storage, and I want good signal like all Motorola phones have.