TBH I only have ever experienced the head rush you talk about when I was a new user, and have only experienced blurred vision when I had smoked way too much. I don't think medical/heavy recreational users experience these things. You keep talking about cannabis like it's incredibly unpredictable and debilitating, but for heavy users it simply isn't. When you vape every day or nearly every day, usually form the same strains and even the same harvest that you're familiar with, cannabis is incredibly predictable.
The way you talk about this suggests peoiple will randomly be surprised by how cannabis effects them, but I don't believe that's a factor for anyone but very light recreational users.
So to answer your question no, I don't think vaping while driving is a huge issue, the only question to me is impairment. If smoking tobacco while driving isn't considered distracted driving or unsafe, neither should vaping. (assuming we allow being high while driving). If vaping/smoking while driving brings impairment to a typical user, then no, they shouldn't do it. But it doesn't matter when they are getting high, it matters if they're impaired while driving.
You don't have to be a new/light user to have a stronger effect one day than the others. You can just be less hydrated, have lower/higher blood sugar/pressure, have another condition/issue starting up, etc.. Just look at the quote below from
@His_Highness
It's just recently that I didn't gauge my buzz sufficiently and found myself behind the wheel when I shouldn't have been. So after four decades of being pretty confident I could drive high, I decided not to anymore and have stuck to my guns. The scary part for me was that it wasn't until I was driving that I realized I shouldn't be.
I wish I had a super low tolerance like a lot of people on here who only vape once a day max. There is a huge difference in how impairing I find cannabis since the beginning, when I wouldn't go outside for a full 3 hours after vaping a few hits, and I am pretty sure I can handle cannabis better than most people I know personally.
However, even on the same plant, buds can have different potency. When you start using different strains, taking different sized hits, etc., it just becomes even more inaccurate. There are far too many chemicals in cannabis to easily measure each dose to make sure it is exactly like the last. If you grind up an entire ounce mix it up really well, and then break it into equal parts, you'll have a more uniform experience with each dose, but that still can't account for biological changes that can cause the effect to vary.
I am not saying it is "incredibly unpredictable and debilitating", but I'm also not saying that it has to be so extreme, for it to be dangerous on the road. Eating food from a takeout container has no psychoactive effects, and isn't incredibly unpredictable or debilitating, but I think people should be punished for doing so while driving. It's distracting, isn't necessary, and can cause death to other people. Smoking/vaping is basically like all the other distracting things people do, with the added psychoactive aspect.
I don't think there is any point in making it legal to get high while driving, because:
1. It's not needed. I've yet to meet someone or even read about someone in a cannabis miracle story, that needs to be puffing away every waking minute. I've met people who claim to need to be high, but that's different. You can be high without being in the act of getting high. If anyone knows someone who will suffer serious medical problems from not consuming cannabis for an hour or two, aside from some discomfort that will be remedied as soon as they smoke again, please do share that with me.
2. The come-up to me is different than just riding out your high. When you are sober, you are sober. When you are high, you are high. When you are smoking, you are transitioning from sober to high, or from high to higher, and that isn't something that needs to be taking place in your brain while you are driving.
Same here... 
