Interesting. In that case, Days could be considered as his first "Hollywood" film. I'd probably still watch a mediocre quality product of Mes petites amoureuses, but I am sypathetic towards the point you made. Let's just consider Malick's The New World which remains a great film no matter what your viewing source is, but the degree of sublimity created by Malick and Lubezki is the highest in a theatrical setting.
You're Van Gogh reference reminded me of the exquisite La Gueule ouverte which was shot by Almendros (Pialat, of course, in case you aren't sure).
"For to see a film as intended by its creators and in its full glory you have to see it on film."
Ideally, yes, but when you consider the vagaries of distribution this becomes a monumental task. That's why retrospectives are so important, even though they're limited to major cities. I can't wait for the full-scale Garrel retro coming up in a few months.
Having seen films on HD/Blu-ray, I'd say that it is an improvement. How long does it take for Criterion and other companies to fully adapt it is another matter, of course.