1. "When do I know when to take someone's critique to heart?"
2."How much thought should I give another person's work before I comment?"
Question 1. When the response becomes sarcastic and is aimed at belittling the person posting the work. Thankfully, apart from a few instances this is rare on this forum, and I have found most criticism to be constructive and helpful (including several comments of yours John, on some of my own offerings).
Question 2. If someone is going to attempt to offer suggestions on how an image could be improved, probably a fair bit of thought would be appreciated...as in "engage brain before opening mouth" (or keyboard in this case). If the intent is merely to express whether the image "speaks to one" or has some sort of "wow factor", then first impressions would suffice. The second instance would probably apply more to "cleaning ladies" or other untrained photographic points of view....however, I do think that the reactions of these sort of people is a very good indication of how striking an image is, or isn't!
On the "equal value" debate....no
they are not!!! I have refrained from commenting on a lot of the work posted here because, quite frankly, there are plenty of people here who are much more qualified than myself that would give better advice. I would hate to give someone a "bum steer" to use the Australian vernacular. In the interests of giving something back to a forum that has helped me out immensely, I have commented where I have felt strongly enough to do so....but it seems bizarre to me to critique work by Russ (whose opinion I have come to greatly respect), and others with years more experience in the field of photography.