Root does not increase background data. All it does is give you more access to the internal files of the phone.
As for using the "use only 2G networks" that won't make any difference since you are using the phone on AT&T, and the CliqXT doesn't do 3G on the AT&T network, so it is always on 2G (Edge).
I recommend using either DroidWall
(Choose which apps can/cannot access data via Wifi or Data Signal [3g/2g]) or APNDroid
(Will stop all background data on cell carrier till you turn it back on).
Both of these apps will require root!
Also Motoblur uses a lot of background data, I recommend installing one of the Android 2.1 Roms that allow you to turn off Blur (Basically Blurless MM278 or ADLXMOD 2.154-2) or even CM7 (Gingerbread).
As for unrooting, why would you unroot!