When i think about things like this I just ask myself.... Do i ever use Yahoo directory to find websites? The answer of course is no.
Why would anyone trawl through a directory when they can search Google Yahoo or MSN. Its sad because quite possible we would all find far better quality web results if we used the likes of yahoo directory or dmoz when searching, but is human nature to be lazy and bung a query to google.
There may be a small benefit when it comes to PR, but not enough to warrent $300. Submit to DMOZ because they are free (if they ever fix their submission problems) and gives you a little PR boost.