I agree that the story itself is not comparable to our lives, but the same can be said for most of the sci-fi or fantasy stories that try to address immortality. I've yet to read a book that's sole topic was discussing the philosophical dilemmas of extended life. Usually, the topic is just an aside to the main storyline (which is thankfully not as often saturated with drama as the vampire genre is).
Fiction is one of our more powerful tools for exploring philosophical concepts. For it to work, you have to create engaging worlds and characters with which to do the exploring. I'm certainly not one for the Byronic hero, but Rice's stories (which were fairly well written and I have to admit that I found them entertaining as a kid) were attempting to humanize an immortal creature so that the readers could attempt to experience a different perspective. She was exploring more than just immortality, so it makes sense that her characters aren't a perfect fit for that topic alone.
Her vampire world certainly isn't any more ridiculous than the world (or characters) of Lazarus Long or Louis Wu. Deep philosophical investigation is hard to do without contrived or ridiculous scenarios. If there's something to be learned from a work (and there isn't always one), then we shouldn't get hung up on the silly details of the story.
Anyway, it sounds like you have in mind a book that better addresses the topic. Can you share? I'm genuinely curious and I've never read enough!