Is paying the money to get in the Yahoo Directory beneficial for backlinking, Google PR, or additional benefits I should be aware of?
Yes. Its worth to submit to yahoo directory. I have some sites there, and I get some traffic, backlinks and I think it will help with the PR next update.
With yahoo you pay around 300 dollars for the review, without being guaranteed a listing. It is probably going to help you in the google serps, but whether it's worth 300 dollars a year merely to be reviewed is up to you.
It is worth it. If money is not an issue, you can go for it. However, be sure that your site is ready. No dead links, no comng soon pages... If it is rejected the first time, they will give you a second chance, and then finish. You need to pay $300 to reapply, so be sure to be ready...
If not for a higher SERP, it would be traffic. I have seen folks get benefits of the submissoin. Your site will do well in Yahoo search engine.