That is true only if you go off-page from your great site and get great backlinks from other great sites, hopefully related in theme.
Well i think if we hav a good pagerank the rate of crawling for our website increases and is updated in a short time
I totally agree with you. I would like to add. High PR = Site is more valuable or reputed in eyes of Google. Well, am I right?
High Pagerank basically makes Google love you a lot more. It helps you rank higher, get crawled more often, etc. Also if you are selling links, while your PR may take a hit, you can get more money from your sales.
To get a good ranking on some keywords, you should only have a good content & design not PR. Why? 1-) Google, Yahoo and MSN track the search visitors' behaves after sending them to your pages. If they leave them from your pages immediately, your page goes down immediately on this keyword. 2-) For every search result, SE's track the number of clicks. If your page doesn't have an attractive title and description it will get less clicks. Less clicks mean low ranking on the search result. That's why when we publish a new content, we get SE visitors in the same day. But they stop coming tomorrow. SE's always want to try the search performances of all new contents on the internet. Because they have to improve their service quality.
It's just a ranking system. Nowadays webmasters get so obsessed about it and to them what matters most is only about PR. In fact, I feel more focus should be put into developing the sites than worrying about checking using different tools to satisfy the curiosity. If you site fully deserves it, then the PR will come by itself.