Tag synonymization requests here on Meta tend to be made by people who have good knowledge of the relevant domain, but lack upvotes on the particular tag. This is good in that it can produce community involvement, but we already have a system for community input; the actual tag synonym proposal and voting features. Those are almost useless for non-headliner tags, though.
The tag system has a good idea about what tags are connected to each other semantically just from their coincidence on questions; there's a "related" list on every tag page. We should use that information to make the tag synonym system work better. If a user knows a thing or two about objective-c, there's a good chance he knows a least a half a thing about nsscanner.
Thus, in calculating eligibility for the tag synonym system, we should count votes on closely-related tags as some fraction of a vote directly on the tag. Maybe half a vote; maybe there can even be a drop-off as the tags become less-closely related.
Credits: This is supported by jmac's excellent post Improving Tag Synonyms, which was in turn sprouted from Jon Ericson's Does the tag synonym suggestion system work? My hat's off to them for laying all that groundwork. The suggestion itself was actually originally made in RobW's answer to Jon's question; I'm stealing it and reposting it as a full request.