Mysticism is a personal revelation, and there really is no way of knowing the source. It can be just vain imaginings or revelation from spirits not from God.(Acts 16:16) You chastised Quix in a previous post about each person interpreting scripture and getting 2000 sects. Well here is the same thing, and no benefit of even reading the scripture. With personal revelation there is the chance of great error as the HS is not the author. To rely on these revelations as doctrine is foolishness.
But, if a person is under the authority of the Church, then I think your concern would be allayed. The Church's mystics, think of St. John of the Cross, for example, or St. Teresa of Avila, have deeply enriched her theology and spirituality. Would you agree?
-A8