I was able to resolve the Sprint Navigation issue by uploading a v2.1.7 cab from the Diamond. For whatever reason, the version in the ROM didn't display the Turn Arrow indicators and prompted me to upgrade every time I started it up. I got curious and installed a cab version of 2.1.7 and the update prompt went away and the turn indicators came back. Seemed to fix everything.

I did, however, end up with two versions of Sprint Nav on the device. I hoped the new install would rewrite the old, but it didn't. ...I also couldn't figure out how to uninstall the old one. [maybe using SKTools or something would work? I didn't try that]

I don't know if this is a decent workaround or not, as I'm still wrangling the "hard rest" issue, but it seemed to get at the problem.