I've tried most of the hallucinogens. I've had some truly amazing exhilarating and profound experiences an acid and shrooms, but also the most horrible depraved fear & loathing and crazy paranoid shit as well. I think they are great if you're feeling strong-minded, some of the thought processes you go through when tripping can be really eye opening. But I wouldn't say they 'changed me' in any way, it's all just life experience. Just DON'T have them if you're feeling low in any way, because the downward spiral can be extremely hard to turn around. I haven't touched either for years because I have no desire to relive the bad experiences I've had in the past.
The most 'spiritual' (for lack of a better word) experience I've had was the first time I had DMT. I smoked it and it lasted about 2 minutes, I felt like I left my body completely, to the point where I forgot to breathe, and the psychedelic visions I had when I was going through it were so amazing that I couldn't even begin to describe them. Completely unlike anything I've ever experienced, like the psychedelia of LSD times 1000 but totally different. Apparently DMT occurs naturally in the body and it secretes in your brain when you die, so the experience of taking it is supposedly like experiencing the visions you see at the end of your life as your brain shuts down. Scary but amazing. I've had it since and the experience was nowhere near as strong as that first one.