Do you know on what grounds Strassman made those claims?
My thoughts on the "inability" to break through...
I wonder, if it is physiological, if any kind of detox regime could help? Lots of seaweed, algae, cilantro, green things to pull out heavy metals that get stuck in the brain (did you ever read about the ways fluoride concentrates inside the pineal?). Just a thought. (and I know the PINEAL is shrouded in speculation, too--but it could make sense.)
Another thing that makes me speculate this way is the extremely antioxidant nature of Ayahuasca. Over time, drinking regularly seems to induce a reverse tolerance. I'm sure there are lots of things at play, but its highly cleansing nature could definitely be a part of it. It's also pretty common, with Aya, for some people to have to drink a few times before they can experience any effects from the DMT element of the brew--she definitely "cleans house" before unlocking the visionary realms. In my personal experience, visions have also become increasingly colorful over time. Partially a spiritual effect? Yes. Partially a learned response? Probably. Partially physiological? I would venture a yes.
SO, anyway, maybe, if all other factors are ruled out (quality of materials, smoking technique, etc.), and a person still can't break through, it might be worth exploring physiology, "cleaning up" and becoming more sensitive.
Has anyone significantly, academically or experientially, ventured into the realms of antioxidants, diet, brain maintenance, and smoked experience?
It does impact oral experience profoundly. There have been reports of potentiating Aya with Melatonin, as well (but this is potentially dangerous and I do not advocate it).