Exporting to a WXR file is not a bad idea at all. If something goes catastrophically wrong then you could create a new empty installation and import that XML backup into you new install.
But if you want to create an even better safety net (who doesn’t?) try creating both a file and database backup of your installation.
https://codex.www.ads-software.com/WordPress_Backups
https://codex.www.ads-software.com/Backing_Up_Your_Database
https://codex.www.ads-software.com/Restoring_Your_Database_From_Backup
Restoring the files is just a matter of putting the old files back; restoring the database is only a little more complicated.
Getting the file and database backup as well as the restore procedure down pat is the best insurance.
In the case of 3.0.1 -> 3.0.2 the database is not modified just the files are updated. If you are running only a couple of extra plugins then you should be fine.
Backup first anyway, that never hurts.
