I found cannabis to have its own impact upon vision but not any form of potentiation, I felt it dulled the trips. I found it suppressed my dreams as well. When I quit (and i do not mean didn't smoke but literally didn't have it in my system and I used to smoke several grams a day) not only did my psychedelic trips become more vivid with increased visual aspects my dreams also returned in vivid detail.
Personally after a few years of experimenting with psychedelics I often regretted using cannabis when I was tripping and I would only smoke at the end of the experience. I can't say I ever found cannabis to intensify the trip. Nitrous oxide, ketamine, and nicotine did. In fact the first time I saw felt disgusted at what cannabis was doing to my, my life and my mental health was the first time I used DMT, a few hits of it and I didn't use cannabis again for 6 months and when I started using it again my approach had changed. I had thought I was using Cannabis to help me live but I had that backwards, I was living to use cannabis and it was nothing to be proud of.
I often found cannabis took something from the experience, dulled it as well as my thinking and feeling during it, however I usually didn't care because I was high. I've often gotten high with friends and then done nothing, just sat around smoking more. It was something to do, it was entertaining but in the end I had absolutely nothing to show for it except lost time. I found that was also true when I was using psychedelics. When I didn't use cannabis during my trips I was more active, more creative and productive. Often with Cannabis and mescaline I would just sit around and not do much.
I liked how weed affected time, hours would seem short, so I would often use it before heavy work or intense martial arts training, but this same effect I liked at times also detracted from my trips, but if things were a bit more intense than I liked I would use cannabis to dull the trip and my thinking. In meditation cannabis did affect the visual aspect of my minds eye and my minds ear, I could lay down and see anything and hear anything I wanted and I would use this on purpose but it wasn't psychedelic.
Cannabis did seem to make my mild HPPD more intense and visual, but only to a degree.
After decades of using cannabis it wasn't doing me any good and I wasn't benefiting from it at all so I stopped using it except for on occasion. I haven't smoked it in years now, but ironically I dream about smoking it, which I couldn't do if I was using it.
I do like the way a small bit of caapi changes the way I see things.
That is a very interesting effect.