Hey,
IMHO you always should learn and master the basics before continuing with the “next level”. Otherwise you will encounter things on your journey which you do not understand but should have knowledge of!
Stack based buffer overflows belong to the basics and have been spotted in the wild ever since they first became public knowledge.
If I check the last submitted entries on ExploitDB there are quite a bunch of submissions for buffer overflows. Mostly for older operating systems or software versions though. This is due to the already mentioned fact that things are getting hardened and more difficult to exploit via basic techniques.
But, do you want to learn all the basics, where it started and how it evolved with only a certain possibility for later usage of that knowledge? Then it’s totally relevant. Look at it as academically and personally relevant.
That said especially in the IoT world many if not most devices there run on older hardware with ancient kernels (2.6.X) and outdated software. Often with not enough space or even capabilities to update those. So for someone researching these devices buffer overflows might be a necessary form of craftsmanship to know because exploit mitigations are seldom present either.
If your target is the hottest new software on the hottest new OS with the latest fresh security updates stack based buffer overflows most likely will not be the way to go (who knows though 
), but the knowledge you learned along the way when starting from the bottom moving to new exploitation techniques will be more than helpful.
TL;DR: IMHO yes.