I am used to receiving undifferentiated comments and I don't mind them. Of course I appreciate it when someone takes time to write their thoughts about my work properly, these are the best comments. Nevertheless, I am not especially interested in receiving critique from someone I don't know and whose photographic ideas might be different from what I want.
I can agree mostly with what Dakwegmo, Oswegan and Scarabaeus have said, however what you call "dumb comments" can just be a message to let you know this person is - still - following your blog. Sometimes I receive an email from someone who never wrote a comment but has been visiting my site regularly since the beginning. Having regular visitors over a long period of time who might write short, long or no comments at all, is a form of positive feedback.
p.s.: When I started with my photoblog, I wrote critical comments sometimes and had to learn that some people just were not able to deal with it, even with constructive criticism. You never know what the person behind the images is like and why they have started their blog. Now I am writing either a positive comment or no comment.