Semantics aside, a Shulgin +4 is defined as an experience that is unrelated to the intensity of the drug (although it often occurs during an extremely intense trip), a state of mind reached that is a trotal breakthrough. I've had three trips I would consider to be +4, and in each of them I was definitely aware that I had reached a special place that would stand out from every other trip. My first was actually not physically a very strong trip compared to where I've been since. it was my first trip, which was on mushrooms, but the novelty of the experience allowed the effects to manifest themselves fully and I experienced oneness. I felt as if I had woken up from my life which was a pleasant dream, and I became aware of a vastly huge infinity of experience, past and future, that makes up my higher self.
I've also had two other experiences where I reached a place of oneness and realization that my life is transient, just a blip in the radar of existence, and those were my other two +4s. In my experience, they involve ego loss and new realization. If you reach the same place again, I would not personally call it a +4, because it's something you've already been to.
The experiences can be life-changing, but it just depends on what you do with yourself afterwards. During the experience, especially if it's your first, you will probably get the feeling that your life will be changed forever. In practice, this is rarely true. But if you apply yourself and the lessons you've learned in that state, and use some discpline, it can elicit positive changes. Then again, so can any experience. A full-on transcendental psychedelic state is just one of those.