I agree completely. What's especially poignant is finding out about and even meeting those that faltered along the same path, both through bloodstains (obviously) and through some of the NPCs.
It really adds some extra weight when you know them personally instead of just hearing a big number.
I actually hadn't thought about the bloodstains until you mentioned them, but you're right. In addition to giving you useful information about the upcoming threats they are a constant reminder that you're not the only one doing this.
That's one of the great things about Dark Souls, so many mechanics further the gameplay in some obvious way while also contributing to the theme in a more subtle way at the same time.