Looking for Android equivalent of Clonezilla / Diskimage / Ghost etc
Root should not erase any phone data.  How do you expect to back up the entire device with only user permissions?  You need root permissions, in the absence of a system-level tool built into the OS or bootloader or a PC-side tool for directly accessing the phone storage (both are very unlikely).  Update: There is now OS-supported backup which an app like Helium can use to back things up without root.

ClockworkMod / Nandroid is definitely not G1-only, there are dozens if not hundreds of supported devices.  It's definitely the best way to back everything up.

I recommend checking out XDA's x10 Mini General forum and possibly the Android Development forum also; read all the sticky threads, they should give you a good overview of all this.  You can do the same for the Desire.