I can’t say I have heard of any organized group mtb trips that focus on self-reflection and spirituality, but I most whole heartedly agree with you that epic mountain biking rides into the backcountry are more than just exercise for me, but can serve as a cleansing of the mind and soul. Granted, I feel similarly about backcountry skiing, rafting, or other pursuits that take you away from civilization. But mountain biking might be the most accessible means to leave the world behind and get in touch with the earth and yourself at a more primordial level.