This is a good thread, and very true. Lots of newbies miss the whole point of traffic, they are focusing more on quantity than quality.
vtabletop gives a great, concise explanation of why you want targeted traffic. And this is where the skill of
SEO comes in. You want to optimize and rank highly for the
right keywords, not just the ones with the highest traffic.
It's been shown that searchers who are closer to buying use
long tail keyword searches to refine their search down to exactly what they are looking for. But by their very nature those longtail keywords don't get as much traffic. It doesn't matter though because as attagirl says, it's better to have less traffic which is qualified than a ton of traffic that isn't.