The Yahoo! directory does hold some credibility, however Basic Submit is a complete waste of money. You are paying for what Slurp does on it's own. If you have not already submitted a sitemap or url list in Yahoo's site explorer do so.
If you have a good placement in the Yahoo directory(high pr page) by all means pay the money and keep it.
As far as paying Yahoo! to get your site crawled is ludicrous, I wouldn't even consider, it does not mean your site will get indexed our your rankings to increase.
Dan