I have a blog that I make sure to never advertise. Seriously, the only "advertisement" I have for it is on my MSN (it may be gone right now, I need to figure out why that ebuddy message won't disappear), so to find me you gotta google it (I try to do fairly extensive SEO and change it from time to time to make sure google still picks me up).
I mostly write reviews, with the occasional rants, and people who want to see my stuff just find it, and generally complain because my opinion isn't the same as theirs. It's just a side thing I do for fun (it's one way I practice writing... my reviews from years ago a basically complete crap compared to my more recent ones, and even then I'm constantly experimenting), it was never really intended as a serious project (in fact, we started with 5 writers and now only I remain).
I don't think it's a waste of time if you enjoy doing it. I don't even care that the only comments I get are on 2-3 year old posts
I say try it out, see if you like doing it and such.