MY, MY! I sure didn't expect this thread to get this long when I started it but I sure am liking the discussion as it goes on. This has been one of the better discussions I have seen around here in a while. We have a UAD-1 card up for bid, gentlemen! Who will make the first bid? Shades of Bob Barker! Come on down! LOL 

Lesthanzero
All great comments.  I recently upgraded from Sonar X1c running on XP SP3 at 32 bits  to X2 on W7 Pro 64 bits, so that necessitated a disk wipe, although I backed up all data on a separate disk.  I think for the small amount of plugins that didn't make the migration fully it'll be easier for me to just redo the tracks than go through what may be a risky reinstall of X1 over X2. 
 
It would be nice if one of the Bakers could comment on this.

While you are waiting for CW staff.

64bit SONAR does not run all the plug-ins provided in the 32bit version. You also lost GuitarRig 4LE and the Beatscape synth, they were dropped from X2. The Content from the Beatscape synth was included in the "Loop and One Shot" installer. So here are some options to think about.
 
Because you are transitioning from 32bit to 64bit AND X1 to X2 you might want to install a full version of X1 32bit. Except I would NOT install Beatscape unless you have already used the synth. If you do install Beatscape, it will install a redundant 4GB sample library. I would NOT install the DimPro that came with X1. Instead, if you used DimPro in your old projects, install the 32bit version that came with X2, otherwise there might be a problem with the serial numbers. This will give you the full environment from your previous installation insuring old projects will open correctly.
 
Perform an advanced install of X1 64bit installing Guitar Rig 4LE only. If you want the Beatscape synth, it is a separate installer and the comments above apply.
 
Or you could perform an advanced install if X1 64bit both the program and Guitar Rig 4LE. If for some reason X2 does not meet expectation then X1 would be available to use with updated X2 plug-ins.

Cakewalk products are backward compatible but some plug-ins included in previous versions may not be in current versions. Also some 32bit plug-ins, notably older DX plug-ins were not ported to 64bit. And occasionally a project just won't open in a newer version. That is why many keep older versions of SONAR installed on their machine. It can also assist when something seems unusual in the current version of SONAR. Then there is the 32bit to 64bit transition issue. A separate but related challenge.
 
It is all fairly manageable. Made easier by not wiping out the historical software that made the projects in the first place. But this is also the reason why some consideration should be given to how projects are stored for future use. Bouncing all tracks to audio just in case plug-ins are not available in the future is not a bad idea. Also if all the tracks are bounced to audio, should the project not be available, the audio tracks can be imported into any DAW in the future.