Thanks for the tips!
No dice. I ensured that settings > advanced > 'Protect SD card' was not checked. Additionally, I went to settings > developer options > launch tools > media provider and clicked 'scan sd card'. It says 'scanning /storage/sdcard1', but doesn't seem to finish or display any useful information. An option to 'Insert 20 albums' causes a 'Unfortunately, Dev Tools has stopped' notice with an 'OK' button. My external SD card is called sdcard0 (by ASTRO).
_3rd Party Apps_
N7 Media Player: Saw nothing by default. I was able to use a setting to 'filter media folders'...when browsing to filter folders, I was able to see that my sd card/media/music/ folder had 500 songs in it...but specifying to play that folder only still didn't help.
Camera 360: This app (without special settings) allows me to view past photos taken with Camera 360, but not other files. I think this is by design for this app.
Dropbox: I use the 'automatically upload photos' option and it seems to be working whether I shoot with the bult-in Camera app or the Camera 360 app.
Astro File Manager: Shows internal and external SD cards and allows me to browse both. I can also verify that 'Camera' and 'Camera 360' are storing new pictures in the same place (external SD card, sdcard0) that existing pictures are located from last phone. Additionally, from here, I found a music file and clicked 'play with' for both Apollo and N7 -- Apollo didn't work at all, N7 played the file, but still shows 0 files in the library. Can't 'next track' or anything. Filter still set properly to my music folder, but no available content except explicit play through Astro.
Gallery: Shows photos I've taken with either the camera 360 app or the stock camera app, but no 'older' photos. Locks up (seemingly) when I try to go to 'settings'.
Apollo: Shows no music and shows no way to specify directories.
Thanks, again, for helping out with this / looking into this. Let me know if I can assist in any way.