A) It can be important to SEO in the sense that it can help get all your content crawled. If you think about a "lazy bot" crawling your content and bouncing halfway through the page only reading a bunch of scripts and tables without seeing what is really of value on the page then yes... it can help.

B) Utilizing CSS can also give you manual control to prioritze content using zones.

C) In terms of PPC: Optimized CSS can also help pages load faster, which can contribute to PPC landing page quality scores.

D) Optimizing code with CSS overall can help your rankings, however I can say from experience that after optimizing some sites built previously on tables and converting the code to tabless CSS has in some cases helped and in others not made a difference at all.

I say its worth doing everything possible in your power to make your site more efficient for users and search engines.

Yes. i agree with Shalom. CSS and DIV are very efficient for better SEO ranking.