How serious are occasional kernel panics? I had a kernel panic about 2 years ago, and another one a few days ago. I haven't had any other problems besides minor software bugs, and I was able to harmlessly reboot after both. I've been told this can mean many bad hardware-related things. Could it just be something relatively harmless, since it doesn't really seem too persistent? Is it worth having it checked out?
The first time you get a kernel panic, it is a reminder to make sure you have a regular backup system in place. Restart the Mac and check that your backup is configured. Check later that day to test restoring a files you need to be backed up. 

The second time you get a kernel panic, decide how you're going to track when they happen. I use a 3 x 5 note card to document things like what I was doing when I noticed it in the date and time. 

Other than that, until you lose real work, the occasional panic/error isn't a real concern as much an annoyance. If you end up annoyed or have recurring panics, gather objective data needed to solve most kernel panics. Apple documents their well engineered process for this:


https://support.apple.com/en-us/HT200553


Once you have a handful of events, checking with support is good since they are in a better position to weigh if hardware is suspected to be faulty or if your panics are software in nature.