Sure, Trac core, i.e. wiki permissions have no inheritance as well, and there are some good reasons for a high degree of privilege separation.
But it doesn't make any sense to give a modify permission without view, does it? In fact, you can hardly do one without the other, so there's no point to try, if not for diminishing the "joy" of hacking a ton of privileges per group/user for each Trac application you have to administrate.
So I speak up in favor of a sensible inheritance like so:
TAGS_VIEW remains just that: TAGS_VIEW
TAGS_MODIFY gets extended to: TAGS_MODIFY + TAGS_VIEW
I'll happily provide the patch or the changeset to accomplish this, if it is acceptable and receives at least two more positive votes from fellow developers. Thanks for consideration.