I have X1 Extended 64 bit on my main computer but have older version Sonar 8.3? 32 bit projects. Will they import in ok to X1?

Yes.
 
Just make sure you rename them so that in the event something does screw up, you can always go back to the old version.
 

Yes... Cake is supposed to be forward and backward compatible. I have not had much problem opening old stuff from the pre-sonar days..(Cakewalk Pro 8 Deluxe) ... some of the older files showed as "corrupted" on the CD and refused to open. Most opened OK but since the synths and FX are totally different they show up as missing..... with a warning that "things may not load properly in this version" but it's just a matter of reassigning the synths you have now to the older tracks.
 
I don't worry about saving the project as new..... I have worked on things started in one program and finished in another, then reopened later in another. It's all good with Cake.

Guitarhacker
but it's just a matter of reassigning the synths you have now to the older tracks.

 
I have to disagree.  It will work indeed but it isn't (always) 'just a matter of reassigning' everything: I've had a lot of problems getting some 32 bit projects opened in my 64 bit DAW because those plugins usually or often also have gone from 32 to 64 bit, which means you will have to add them as new synths (which can already be quite some work)... which means you will have to figure out which presets you were using in the old project... which can be hard if not impossible because you can't open those old 32 bit synths to see what you were using at the time! The same may go for effects. 
 
I had to reopen a lot of 32 bit files for a cd I had to create in Sonar 8.5 64 bit and I ended up reinstalling Sonar 6 and 7 in 32 bit plus all the 32 bit plugins just to solve all the converting problems... (I opened the old project in S6 and S7 32 bit and then I was able to see what presets and settings I used, etc. and 'copying' all those settings was sometimes a LOT of work (like a lot of keyswitches I had programmed in RealGuitars...)).
 
So yes, you can open old 32 bit projects in Sonar X1 64 bit but be prepared for quite some work! 

I have remedied this problem by loading Sonar 7 in 32-bit mode on my computer. The old files open as they should with the old plugins (provided I have the right ones installed). 
 
I've since accepted that everything in the 64-bit world has to start from scratch :(

Well I have yet to make the jump to light-speed (aka 64 bit applications) so that part of the equation has not been a concern.
 
However, Point taken.

This is definitely not the norm. If you had to reassign synths after opening the project in 64 bit then the 64 bit versions of the synths in question were not compatible with their 32 bit version. The vast majority of plugins are fully compatible across 32 and 64 bit. Its a requirement that they load in both versions. Everything saved in the project file is 100% compatible with both flavors.
 

hellogoodbye
I have to disagree.  It will work indeed but it isn't (always) 'just a matter of reassigning' everything: I've had a lot of problems getting some 32 bit projects opened in my 64 bit DAW because those plugins usually or often also have gone from 32 to 64 bit, which means you will have to add them as new synths (which can already be quite some work)... which means you will have to figure out which presets you were using in the old project... which can be hard if not impossible because you can't open those old 32 bit synths to see what you were using at the time! The same may go for effects. 
 
I had to reopen a lot of 32 bit files for a cd I had to create in Sonar 8.5 64 bit and I ended up reinstalling Sonar 6 and 7 in 32 bit plus all the 32 bit plugins just to solve all the converting problems... (I opened the old project in S6 and S7 32 bit and then I was able to see what presets and settings I used, etc. and 'copying' all those settings was sometimes a LOT of work (like a lot of keyswitches I had programmed in RealGuitars...)).
 
So yes, you can open old 32 bit projects in Sonar X1 64 bit but be prepared for quite some work! 

I was about to post the same thing Noel. I have only had a problem with missing plugins. Plugins that I no longer use. One of these is Vsampler.  However, if I have a 64 bit version Sonar will load that even when it was made with a 32 bit version. Some will even ask if you have both versions. 
 
Its possible that the system has changed so much when you moved to 64 bits that old projects can't find plugins that will match. This is not Sonar's fault its bad planning on the user's end.