Do we need a tag for each punctuation mark when there is already the tag punctuation?
From the use cases point of view, it seems unlikely someone would want a cloud of 'comma' related entries for polishing their skills with commas; or the dreaded colon v. semi-colon learning curve. However, as my poor skills of punctuation may show, I can imagine someone looking to improve their overall knowledge of punctuation and its usage.
As such, it seems to me that by consolidating specific marks in a 'punctuation' tag would be preferable to letting questions about individual marks hang out on the fringe with a useless tag. Obviously synonymizing (sp?) tags is another option, but if it's a black/white choice I find 'punctuation' to be more useful.