While I completely understand the need for prudence when you are running a commercial studio with the clock ticking and paying clients, I think sometimes people tend to be overly paranoid about the potential for problems with software releases.
Generally speaking I think you run a greater risk of system instability when doing a Windows update than with installing a new version of SONAR. The cross dependencies when you install a new version are completely minimal and if anything, 99% of the time, installing a new version can make the old version run better since the shared components can contain bug fixes. If you do use backup software you could save a snapshot and restore in a few minutes if you really needed to but that is not even necessary. The only things that are common between X2 and X1 that are relevant are the following folders:
C:\Program Files\Cakewalk\Shared *****
C:\Program Files\Cakewalk\VstPlugins
These folders contain common components that are shared between SONAR versions including plugins. The program itself is always in an independent folder under C:\Program Files\Cakewalk and any application data lives in discrete folders under the windows "AppData" folders.
If you want to be even safer just back up the entire C:\Program Files\Cakewalk folder and if you do ever need to get back to all the prior state in a pinch, restoring that folder will bring back all the old common stuff. You could even copy and rename the folder to keep both versions online. I frequently do this when developing if I want to test behavior in a clean old version.
I do understand that many users are not tech savvy when dealing with Windows but there really is no voodoo happening when you install a new version of SONAR. The old version itself always stays intact and the new version is installed in a brand new location, other than the common files listed above. There is one more shared thing - the VST inventory, but all you need to do is a full rescan to rebuild it again.
If you take these simple precautions there is really no need to worry about installing a new version as long as the old one is kept installed.