Yes, there are other ways to install Google Maps Navigation. I'm working on a new version of Nav Launcher that will include a simple install process. It should be out in a day or two.
For now, you can just go into a rooted terminal and run "mount -o remount,rw /system", and all the commands on the main page, without the "adb shell". The "adb uninstall" can be replaced with "pm uninstall".
Lastly, you can download the new apk file in the device's browser, and install it that way.
Hey, thats too bad. You can use fastboot to flash the original images if u have them. If you flash the original boot.img, system.img, and recovery.img you will loose root.
The only question is, can u fastboot?