SP = sensory perception
MP = mystical perception
One of the questions people have about MP is this: how exactly does it differ from SP? It seems as if the characteristics of MP are generally the same as those of SP. For example, a heavenly vision and/or message constitutes vision and audibles, which are thought of as defining characteristics of SP.
Before we attempt to distinguish between the two, it should be asked: does this hurt the case for MP or help it? It seems to me that the arguments against MP can be used equally against SP. If, for instance, Paul hallucinates a vision of Jesus, where the vision of Jesus is not veridical, then that is an argument against a particular instance of MP. The problem with this argument is that it can also be used against any instance of SP. If I observe a flower in a garden, and my vision has an impression of a purple flower, it could also be the case that I am hallucinating a non-veridical color, or even a non-veridical garden.
This brings us back to the age old question: how do we know what is real? I think there are things we can know with certainty (e.g. the existence of the self, the existence of God, and the fact that the self is not God), but that doesn't necessarily help us determine whether most instances of SP are veridical. In fact, it might even be argued that the success of SP entails the success of MP.
Differences in perception are also appealed to in discrediting MP, but once again, the same argument can be used against SP. Although I may be seeing a purple flower, someone standing at the opposite side of the garden may see the same flower as a white flower. Yet, this doesn't necessarily mean that either one of us should abandon our beliefs about what we perceive via SP. Perhaps there is a defeater for one of our beliefs. If I discovered that there is a light shining above the garden that, when someone is standing at a certain angle, makes white flowers appear purple, then that would give me an incentive to abandon my belief.
So, the skeptic of MP could reason that while there are available defeaters for instances SP, there are not available defeaters for instances MP. In other words, one's beliefs need to be falsifiable in order to be veridical.
Of course, this line of thought is troubled by at least two factors. 1) The principle that every belief must be falsifiable is it itself not falsifiable, so it appears that this objection to MP is self-refuting. 2) The criteria for falsifiability may be applicable to MP, after all.
One way of falsifying some instance of MP is to show that it is contrary to other things we know. If, for example, S has an experience of MP in which it is stated to S that torturing children for fun is a good thing, then given what is known about proper moral behavior, S is compelled to reject this instance of MP on some grounds (psychological, demonic, etc.).
Yet, it also seems to me that there are solid confirmations of MP. Say that St. Teresa of Avila has an experience in which God tells her that He loves her. This is consistent with God being the greatest conceivable being, so barring any defeater, her experience of MP may be veridical. I also believe that the arguments of natural theology establish God's existence, so any instance of MP that is consistent with what we can know on these grounds may also be taken as veridical.
The skeptic can, on the other hand, appeal to something like the logical version of the problem of evil, which states that the existence of God is logically incompatible with the reality of evil. Of course, I don't think these arguments are at all successful, given that God may have a morally sufficient reason for allowing evil. Plantinga, I think, put the nail in the coffin of the logical problem of evil.
It seems, then, that the reasons for rejecting MP work equally well against SP. If, therefore, SP is accepted in spite of skepticism, there remains no additional reason for rejecting MP.