There's two issues here:
The first is fairly easy to deal with most of the time. Purely useless tags such as "specific-spell" are going to crop up on a regular basis. Most users don't really know or care about tagging, and are just typing things in to make the "tag required" error message go away.
MOST of the time, simply deleting the low-use tags as they crop up should be fine. Occasionally the question owner will squawk, which is the only really tricky case there. I'd say just leave it for the reaper (excess tags are annoying, but don't seem to be very annoying). But a case could be made for getting more aggressive...
The deeper issue is what to do about tags like "spells," "feats," or "rituals." These are kind of meta-taggish (they don't have a clear meaning without a system tag). I'm not really sure what the best option here is... I can see searches for "Pathfinder spells" or "dnd-3.5 feats", but only just barely. And "Exalted Spells" is going to mean something much different than "dnd-3.5 spells"...
Of the tags listed, I would personally get rid of skills, powers, rituals, and feats as too redundant to their parent tag (and I'd probably synonym monsters->adversaries). But that's purely my take on it.
Finally, a shout-out for the tag synonym page (linked at the bottom of the "tags" page): https://rpg.stackexchange.com/tags/synonyms
There's a couple synonyms pending that I'd like to see some movement on :)