All of the questions tagged with ssid are related to wireless-networking. There are only 4 followers of ssid. All experts on wireless-networking should be experts on ssid. I see no purpose of the ssid tag. Should we burninate it?
Yes, ssid is a subset of wireless-networking, but it is a meaningful subset.
Whether each question using the tag is actually a question ABOUT the ssid is irrelevant. Some questions CAN be mostly about the ssid and therefore the tag is a meaningful distinction between it and other aspects of the broader wireless-networking.
Keep the ssid tag.
While there will be clear cases where the ssid and wireless-networking tags will have synonymous meaning, the function of an SSID within the realm of wireless networking is distinct enough to merit its own set of questions and specific expertise.
There are a lot of wireless-networking questions. To merge the ones focused on SSIDs into the larger pool would make them less accessible to both question askers and answerers.