Everything in moderation - including moderation.
I don't consider it 'taking breaks,' nor 'cheating.' I've gone from eating wheat almost daily to eating it once a week at most. And it's in small doses at that. I no longer eat factory meats. I buy organic when it's available.
It's a blueprint, not the Bible.
As to plateaus, I find that shaking up things will usually break them. A day of increased calories. A five mile walk done at a brisker pace. A day without animal. A day of all animal. My intuition tells me that plateaus are the result of adaptation, so I blast my brain and body with something different to smack that adaptation in the face. It almost always works.
"Right is right, even if no one is doing it; wrong is wrong, even if everyone is doing it." - St. Augustine