I have X3e Producer running beautifully and haven't touched X2 Producer since I installed it (except to convert over a few works for easier use in X3). 
 
My only concern is that when I uninstall X1 and X2, I'll inadvertently lose something I really need, like all my plug-ins. (X1 Producer's also still on the computer; don't ask. You wouldn't believe what the last seven years of my life has been like. Somehow uninstalling dormant programs has not been a priority for me. This summer, however, I've got the time to clean up the computer.) Does anyone have any bits of wisdom to share with me about this? Tales of disaster occurring or, more hopefully, avoided?    
 
Thanks for any suggestions offered....

All I can suggest is to back up any directories with VSTs in, and whatever data they refer to. Then do the uninstallation, and check the plugin manager to verify that nothing has gone missing. (And if so, restore the relevant files.)
 
Sadly Sonar doesn't do a good job of keeping things in consistent places, and Windows doesn't enforce this either, so you'll end up with stuff strewn across Program Files, Program Data, Appdata/Roaming, My Documents... all you can do is try to familiarise yourself with where everything is before you proceed.

I recommend keeping X1 and X2 on your computer. They can reside side by side with X3 without any issues. I have X2 and X3 installed on my new computer.

I would leave them! I have every version since 8.5.1 on mine. Sometimes makes it easier to load those old projects from several years ago to tweak or re-mix. I have had clients come back with projects that were several years old to "modernize" the tune. Just load it in to the old version and you should have very little problem as long as you still have the legacy plugins.

Thanks for the comments.
 
I'm thinking that there is much wisdom in all, but, since I really do not have the "need" to free up the HDD space, maybe I will just leave X1 and X2 on the drive.
 
Offered in the spirit of "don't fix what isn't broken".  
 
Thanks again!

aint broke?.. don't fix it!.. :D

Mystic38
aint broke?.. don't fix it!.. :D

You know, I'm learning that.