I’m new to Cubase and now facing my first upgrade. Does Cubase fall into the category of applications (and operating systems) that generally benefits from a clean install? Or, does it have a history of upgrading cleanly without caveats?
I have no problem performing the extra steps of backing up prefs, uninstalling, reinstalling, etc. I just want the most reliable option.
Any advice is appreciated.
In the time I’ve used Cubase (about 6 months), I’ve always upgraded without doing a clean install, and have never had an issue. C9 is as stable as C 8.5 for me, with no additional issues aside from the ins and outs that we all gripe about here. 
It is a clean install anyway…it isn’t upgrading your last version. That will remain and C9 is installed alongside it.
It does share content and it should (but sometimes doesn’t) bring over preferences from a previous version that’s still installed.
For the most part just running the C9 update is all you need to do.
If Cubase was upgraded you would not be able to use the previous version. As Grimm pointed out you have another, separate version of Cubase to use. C9 imported all my preferences, presets and my recent project history in 8.5. So it is in fact a clean install. I
Thanks, everyone. Upgrade it is.