A blog on credit cards, insurance, or another high paying term could make quite a decent coin on 100 uniques per day -- some other sites might struggle to make anything on that.
Money aside, how successful your site is in terms of spreading your message really depends on what message you're trying to spread. You could have an authority blog on a small niche which might be considered the "go to" place for information on that niche which gets a low number of uniques (because it's "that niche") or you might get hundreds of uniques per day and not really have a blog that's anything special (eg. a blog on the broad subject of how to make money online)
In summary, I really wouldn't focus on the uniques. How good of a job are you doing at having your message heard? That's success imho.