Paid for templates

You ought to ask the guys who are advertising those services.
A paid template in general, no.

comments along the line that a paid template benefit is increased SEO rankings

The answer to this is – Maybe, or maybe not. Sounds vague, but that’s about the best that you can say with that. The ability of a theme to do SEO depends on a lot of different measures, like how the page is layed out, how clean it’s HTML code is, how the structure of the tags breaks down and a few other things. Overall these things are a relatively small aprt of SEO. As much as a good theme can help boost your SEO a bit, setting up permalinks correctly, and writing good human-readable keyword-rich content for your site will always boost it more then any theme ever will. But… they don’t want to tell you that because it doesn’t help sell their products. 😉

I’d get a theme depending on how well the look, feel and functionality suit the purpose of the site. SEO can be done later, and it’s easy to implement yourself using a child theme if you really need to.