I have lingering doubts about the import to which you attach Spinoza's mysticism though, for I'm of the conviction that his pantheism was only the best such a mind as his could manage in his age, scientific advances being what they were. Like the deism of later thinkers, his mysticism was the ne plus ultra of philosophical understanding in his day. I'm persuaded that Spinoza, living, would have cast off the imbecility of supernaturalism completely. But I'm a partisan. I invite your thoughts.
Perhaps Spinoza himself may well have cast off his mystical thoughts, or perhaps he would have given them a different emphasis - ala Jung who is a contemporary intellectual giant that is thoroughly enmeshed within the mystical tradition.
For my part, I think the import lies not with the individual practitioners or thinkers but with the mystical tradition itself. This tradition is both timeless and displaced, there is no one definitive starting point and so no one definitive state of doctrines or rules. There is only one idea and this idea fuels the entire purpose of its practitioners - the overwhelming, unending, desire to achieve union with "god" and to swim in that infinite absolute as an unrecognisable drop amongst the ocean.
Now, there are many caveats to this tradition. I think it cannot be dismissed with as much arrogant glee as orthodox religion because the tradition does not attempt to rationally prove itself - it rather sidesteps the entire rational system and proclaims that the absolute, transcendent reality can only be experienced and not logically known. Furthermore, the mystic states that there is not but one path to this enlightened inner realm but an infinite many, and every holistic subject (you and me) must undertake their own such journey for themselves. There are certain archetypal features of such an undertaking, as Jung has pointed out in his study of spiritual alchemy and the collective unconscious but these are only broad motifs and do not all apply to every individual.
Can it be that such an experience exists and can it tell us anything about the world?
I think the answer to the first question is a definite yes. Whether or not this experience is of anything real, it cannot be doubted that many around the world from all ages have felt the ineffable and the transcendent. One can list countless hermetics, gnostics, sufis, yogis and so on who have at one time or another claimed to have experienced the mystical. The experience itself is a reality, what the experience has to tell us about the cosmos is the second question.
To this I cannot give anything but an agnostic answer. How is one to know what a mystical and spiritual alchemy entails unless one undergoes it oneself? How can we know what is meant by the "enlightenment" that is so madly desired by the mystics of all ages? I think to answer this question, you have to experience it for yourself because it cannot be brought into collective, social scrutiny - it can only be discovered for yourself. As Plato would have it, only you yourself can escape the cave and reach the mystical pinnacle of truth and beauty and wisdom.
I do not know how much truth there is in these ideas, I am merely standing at the doorstep and asking that whatever is behind that door be given a fair hearing and not dismissed out of hand just because those that have stepped through here have called themselves "religious" and/ or "mystical".
Topic: Does Atheism Poison Everything?