Rooting is required to add Google Market and Live Wallpaper because you need to be able to mount the System folder with write permissions to install those Apps. If you can live without those, I see no reason to root. With Amazon, there is even less of a reason. (Although Amazon adds DRM to all the apps, so once you get apps from them, you are stuck with them forever...even free apps.)
Ermine is Android 2.2, where Dingo is 1.6, so updating to Ermine gives you access to any apps that require Android 2.2. EnTourage also fixed a few bugs with Ermine. Android 2.2 (called Froyo) improved batttery life, and was generally considered faster than 1.6.
On the full sized edge (which I do not have) I understand that Ermine might have introduced a few bugs. I have a Pocket eDGe and updated to Ermine and Rooted ten minutes after taking it out of the box so my Dingo/non-rooted experience is minimal. I can say I have been going 4 weeks with no problems.
If you are rooted, be sure to follow and instructions exactly when adding any features that require root. The reason we don't have root out of the box, is so we don't mess up our eDGes! Another advantage to not rooting is you are safer from poorly written programs and malware (viruses).
In summary: Dingo is android 1.6, Ermine is 2.2. Both can be rooted. Rooting gives you permission to modify any file or folder on your device.
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