yes, definitely good as you will gain backlinks from different IPs website. But will the article rank ? not likely if your article is duplicate.
No, almost all article directories only allow to submit original and unique articles, else your article will be removed.
Submitting to many article directories is more for link builidng than for traffic. However, the links may appear a few months down the road. I doubt the search engines will index all the 450 directories at the same rate.
I would go for 3-5 article directory with spinned articles. My highest recommendation is Ezinearticles ArticleDashboard GoArticles ArticleDatabase For the rest of the site, I go whatever just to gather links. Of course the more the better for this purpose, but quality doesn't have to be good.
Yes its worth it. It increases PR & also results in back links.It also increase traffic to your site. But all these thing totally not depends only on directory other factors are also there.