The tags are almost completely separate. Merging them sounds inappropriate.
Setting up and troubleshooting a wifi link is a OSI level 1-2 issue ("I'm losing packets from my neighbour's wifi because there's a wall in between!").
Our use of the networking tag seems to be overwhelmingly about levels 3-5 ("I can't discover my friend's server! How can I do port forwarding?").
In English, you can have networking issues regardless of whether or not you're using wifi and wifi issues normally translate in issues that go beyond any one program or video game and are thus trivially easy to identify as such. They're separate layers that are only loosely coupled. The issue, in short, is much simpler than the justification I've just given. We have been consistently using those tags.
There was only one question tagged networkingand wifi; while the asker seems convinced that the only change he made was in level 2 (wifi password), this affected higher levels too so... I think the use of both tags is justified in the end, and also a further argument against merging.