Especially in infrequently used tags, more general is better. "Well my question isn't quite about the astral plane it's about..." is the immediate issue from the next question about astral phenomena. And then we have a fistful of astral tags all running the risk of deletion because they don't have enough use.
It is fit for use right now. "I have a question about astral projection, or astral travel, or monsters on the astral plane, or whatever... I start typing in astral... Oh look there it is, great." If you are searching for info on the astral plane, and you go to tag:astral, you're not exactly overwhelmed with 100s of superfluous questions.
Our tagging is not a logical taxonomy. It is an emergent folksonomy, where it modifies to fit real needs and real numbers of questions, not a sense of logical rigor.
There are no problems with the existing tag, and none cited in the question, therefore no action should be taken. (By problem, I mean things that are affecting its usefulness in practice for questioners or answerers.)