So... despite having more than enough points in a "super-set" tag, I was unable to make the suggestion.
I'm assuming that SE sites have no concept of related tags but would like to suggest they may be useful. It doesn't have to be a tree; it could simply be a "similarity" or "overlap" weighting between any two tags.
This could be used as a multiplier when calculating whether the user has sufficient points to edit the tag; for example: .net -> 0.2 -> .net-4.
Therefore, when calculating the points for .net-4, look at all connected tags and add up
Score * SimilarityWeighting. In the above example, my .net-4 points would be
46 * 0.2 = 9.2 for the purposes of calculating permissions.